Error 21 is related to the PRELINKING=yes in one of the config files of your system. This is a known issue with Cedega on the 2.6.9 and 2.6.10 kernel.
Getting this fixed it quick, simple, and easy.
Just a I tip I learned from doing it my self...some of the commands they show you don't show anything back to you...so its not like you can see that it worked till you try it.
nfsu2 demo is the only thing that was tested in cedega, but it did work. Not sure if you subscribe to Transgaming.com or not but you should add it to thier games database if you do.
Just follow the intructions on this link, hopefully your running FC3...cause this is quick and easy. If you are using Fedora Core 3 don't bother with the HD mounting stuff they have listed.
http://transgaming.org/forum/viewtopic.php?t=1325
Hope it helps. If not just let me know I'll give you a hand!