you could have a look at this: LinuxBBQ Rocks!
although it is currently still in development. at any rate, the base it is, uhh, based on, linuxbbq, is by default light and bloat-free, and should work on most systems because of the non-free drivers included by default. read more here: http://www.linuxbbq.org/
this should be especially good for old systems like yours.
as an aside, when it comes to Linux in general, it is important to realize the community is an integral part of the distro. this might be one reason to not go with Ubuntu, as its community, however large, is not a very friendly one (in my experience, the larger the community the less friendly it seems to get). in this case you might again want to check out linuxbbq, or try something like Crunchbang Linux which is light too and has a good community behind it as well: http://crunchbang.org/
if you got more questions, please ask. good luck!
(aside from that, everything fladd and carmazine said here is very good advise as well)