I just read the tweaks on http://www.musicxp.net/ and I can say that many of the twaks there is realy nothing that will tune up the performance of your computer or make any main difference. I suggest you do NOT do any of these tweaks if you are not 100% sure of what they are doing and realy want to tune your OS in this way.
I’ll try to explain the tweaks very fast here:
1. Processor scheduling should be set to background services and not Programs.
When you have this set to Programs all foreground processes receive a small priority boost so they become more responsive to the user. The sacrifice is that the background processes will get alittle less CPU-time. When setting it to background services no priority boost will be done so the CPU power will be shared fairly to all processes.
This is good for example audio-drivers, so this tweak is higly suggested.
2. Visual effects should be set to a minimum.
That is a tweak you SHALL do. It will increase the performance cause the the computer doesn’t need to put resources on small shades and animating menues etc 
3. Switch Off Desktop Background Image
This is also a good thing to do, saves memory and cpu…
4. Disable Screen Saver
Yes, also good. Saves memory and cpu. Some screensavers is realy CPU agressive…
5. Disable Fast User Switching
I doubt this will increase any performance but I think it is still a good tweak. Makes XP act alittle more like Win2k = good 
6. Switch Off Power Schemes
I can’t realy understand why they think you shall turn off power scheme for your monitor… only sounds stupid to me. I can understand why to do it for your HD’s but not for your monitor…
7. Switch Off Hibernation
Only use hibernation if you realy need it. If you use it it will eat as much harddisk-space as you have physical memory.
8. Activate DMA on Hard Discs/CD ROMS
Ofcourse. This shall be default but can fail on some setups. This will make harddisk-access to consume less CPU.
9. Disable System Sounds
Yes, do this! This will not just mean that you will get rid of all the anoying M$-sounds, it will also speed up soem processes (login, logout etc) and will save you some memory…
10. Do Not Map Through Soundcard
This isn’t realy a nessesary tewak and I suggest you do not do it if you don’t need to do it. The setting will disallow Windows from using your audiocard while you are recording. But in the previous tweak you just turned off windows system sounds so I realy do not see any point in this. Some people have problems when changing this setting so just leave it if you do not have any problems.
11. Disable System Restore
System Restore can be a good thing. It will consume lot of harddisk-space but can save you lot of work if something bad happens in your OS. It is realy not recommended to turn off this, but it is all up to you. 
12. Disable Automatic Updates
Automatic Updates can be good if you are connected to internet 24/7 (as I am) casue then you will get the latest security patches as fast as they are released and this will keep your computer a bit safer. It will probably not save you much cpu nor memory to turn it off, anyways I still have it disabled cause I do not like having my computer connected to Microsofts servers withou my contoll

13. Startup and Recovery Options
Do this setting if you are not running your computer as a server! It will prevent the computer to restart if you get a BSOD (BlueScreen of Death), and means that you will see the full error-messages whenthis happens…
14. Disable Error Reporting
This is realy not nessasary. If you (as me) think it is annoying to get this messages and do not want to send (personal) info about your computer to Microsoft I suggest you turn this feature off.
15. Disable Remote Assistance
This tool is used to allow other people to login on your computer and help you solve problems remotely. To have it enabled is a security-risk so I suggest you turn it off and only enable it when (and if) you realy need it.
16. Fix Swap File (Virtual Memory)
Yes, do this, they have also missed to say that you shall set both min and max to recommended size (*1.5 od physical memory)
17. Speed Up Menus
Not realy nessasary. You will get slightly faster menus, you will probably not even recognize it
But why not? 
18. Disable Offline Files
You can do this if your not planning to use this feature.
19. Disable Remote Desktop
Remote Desktop is a exelent tool. If you own many different computers and have them connected in a network, or if you want to be able to connect and use your computer remote I sugest you take a look at this feature. If you don’t, you can safely disable this feature.
Just remember to set up your firewall correctly if you plan to use it…
20. Disable Internet Synchronise Time
Why? I can see no good reaon in disabling this feature. Especially if you are connected to internet 24/7… You shall change time-server though, microsoft is evil, do not use their server 
21. Disable Hide Inactive Icons
The only reaon why to disable this feature is if you do not like it. To disable it will not save any cpu nor memory. So I suggest you do not disable it untilll you realize that you realy do not want this feature. I use it and like it…
22. Disable Automatic Desktop Cleanup Wizard
Same as the previous.
23. Disable NTFS Last Access Time Logging (NTFS File Systems Only)
On NTFS volumes windows updates the Last Access time stamp every time an access is made to the harddrive. With a large number of directories this can cause a decrease in performance. I have personally never noticed any significant diference when changing this setting so I suggest you only change this if you think you will need it…
24. Disable Notification Area Balloon Tips
The Baloon is realy annoying so why not, but do not expect any significant performance-increasing
25. Disable CDROM Autoplay
hmm. why? Some programs can have some troubles with auto-playing cdroms but thouse are very rarely so I sugest you only do this if you either do not like this feature or install programs that recommend you to turn this feature off.
26. Disable Disc Indexing Service
yes, the indexing-service isn’t realy something nessesary if you do not search alot on your computer.
And finaly, when it comes to ACPI it is better to keep this setting as it is as long as you do not have any serious irq-sharing problems. It is even better to try to move the PCI-cards physically to another slot before tou try to change this setting casue if you change this some strange things can happen to your computer and if you are not a bit experienced in irq’s etc you can get even more problems than before 