Can't enable Desktop Effects in Ubuntu 8.04

Hello there Linux community.

I'm not a "new user" of Linux, (been using it on and off since last year) though I'm not exactly an "experienced" user either. My problem is that I'm trying to enable desktop effects so that I can use the desktop cube extra (by the way I run Ubuntu 8.04) and whenever I try to enable my Desktop effects, it just tells me that I can't. "Desktop Effects can not be enabled". My rig is an eMachines PC with an ATI Radion x1300 PCI express(much rather be using an nVidia 7 series, but such is life), an Athlon 64 processor, and 1 GB of RAM. Any tips or suggestions on this issue would be appreciated. Thanks.