i'm thinking about buying a Dell Optiplex P4, GX280 w / 40 Gb hard drive, 512 RAM "Video-On-Board: AGP Integrated" and 3 PCI slots for a friend whose computer i was unable to upgrade to our new, shiny, KDE 2010 (it was/is a PIII w/256 Mb purchased on credit from Telnor here in Mexico about 2 yrs ago). i had placed PCL 2007 on it but the lease ran out and she wanted some more card games on it so, dumb fred decided that it would take PCL KDE 2010. Ha, ha. Wrong. So now i've had to tell her i can't get here old system to work; it no longer has Win on it and i haven't been able to get OpenBox, LXDE or i don't know what else to load, much less to run.
I used to have a GX280. The maximum RAM it will hold is 2GB. You'd do well to put that much in. Using an AGP card, instead of shared video memory, will help a lot. The shared video memory will be subtracted from whatever RAM you have. If you can't find or afford RAM for it, PM me. I probably still have those sticks.
As for the other machine, I'm currently running PCLOS 2010 LXDE edition on a Dell Dimension 4100, with a PIII running at 800 mHz. The machine has as much RAM as it will hold, which is 512 MB. To get more performance, I put in an nVidia AGP card with 512 MB of video RAM. The LXDE desktop is very snappy, although IDE disk speeds are fairly slow.