I'd opt for a lightweight distro. I'm running a desktop with the same specs, CPU and RAM-wise as you, and am more than happy with Anti-x. I've not had to re-install once, (used it for over six months), and have everything working as I like. It has a small and user-friendly forum, and makes use of debian-based repositories - in other words lots of applications for you to try.

I wouldn't recommend running a KDE4 desktop - which is distinct from the distro - as it will likely be a menace to your CPU, and be too slow.

Just out of curiosity, the iso of Fedora with Gnome is 675MB while the iso of Fedora with Xfce is 698MB. Are you sure that Gnome is the more resource intensive!?

space on disk does not equal space in RAM nor CPU usage

I have Fedora 14 with GNOME on an 9 year old desktop with 1Gb RAM and an Intel Celeron Processor. It runs just fine. XFCE will probably run lighter, but if you prefer GNOME it shouldn't cause any problems...
You could try out the Linux Distribution Chooser at http://www.zegeniestudios.net/ldc/in...firsttime=true It recommends a distro out of a selection of popular ones based on the answers you give to related questions...