My laptop is an Inspiron 5100, and for the longest time I couldn’t figure out how to get “Desktop Effects” (compiz) going in Ubuntu. I didn’t think my video card (Radeon Mobility 7500) was compatible, but it turns out it is. I just needed to change a couple settings.
First, I put the following in
<option name="allow_large_textures" value="2" />
/etc/X11/xorg.conf I changed my
16. Finally, I restarted X with Ctrl-Alt-Backspace, and enabled compiz in System → Preferences → Appearance → Visual Effects. Voila!
I found these instructions here.