As for your "problem opening DISPLAY" in rxvt, something in your scripts is broken and erasing the $DISPLAY variable. You can test this by typing (assuming you use bash)
export DISPLAY=:0
someXcommandhere

:0 is the first local X server. if you have more than one X server, they're :0, :1, :2, :3 etc.

It should then run. If you're using bash, check /etc/profile, ~/.bashrc, ~/.xinitrc, ~/.xsession for anything unsetting or overwriting the DISPLAY variable.

Hmm... if it only has a problem in rxvt, you could either not use rxvt, or check your shortcut you're using to open it for odd parameters that would reset the environment variables.

RE: Dumb newbie issue: firefox-0.8 cant run after installed
 

Strange, I've just hit that same problem on SuSE 9.0 after a fresh install, same with evolution, the processes are in sleep, but no output. Permissions etc. are all OK, no errors relating to the display are seen either, running strace doesn't show up any funnies either, ldd on the binaries is also OK. They both used to be OK on the original install. Mozilla, FlightGear etc. all run fine. PUZZLED!
Regards
Sid.