disabled the font-antialiasing.
http://www.renoise.com/board/index.php?act…=ST&f=14&t=4437
I did this on my AMD, and suddenly all works as it should. I have no idea why and I dont know if it will work for anyone else, but it worked for me. phew.
christ, forgot to post this :
while the gui is alright now, the loading still takes ages … over 5 seconds for a 2 mb wav file … 
I believe Taktik explained that the loading was slower to save system resources.
http://www.renoise.com/board/index.php?act…399eb47ab88b7a2