svchost.exe - Don't mess with these guys. They're important.
nvsvc32.exe -kill
wmiprvse.exe - Manages windows updates, kill it if you'd like.
taskmgr.exe - Taskmanager you're looking at for this list, close it when you're done.
wuauclt.exe - More with the windows updates, kill.
firefox.exe - Close it if you see it open while not browsing the internet.
DkService.exe - This is associated with Executive Software Diskeeper, kill or keep, your call. I'd kill, though.
svchost.exe - Seriously, don't mess with svchost.exe
nSvcLog.exe - nVidia logging program. Kill if you're not using it.
nSvcIp.exe - Kill if you want.
nTrayFw.exe - nVidia services tray. Not useful if you're not using it. Go ahead and kill.
avgcc.exe - Virus protection, kill it if you're feeling lucky.
Apache.exe - If you don't need Apache server open, you can close this. Unless, of course, you're playing an Apache game, then this will likely be your game.
explorer.exe - Close this and your desktop, and your explorer(not firefox) windows go bye-bye. Open a new process called explorer and the desktop comes right back. Can be useful if you don't want to restart your computer when you install something that tells you you'll need to.
wscntfy.exe - Windows Security center. Kill if you'd like.
avgemc.exe - More AVG anti-virus. Kill if you're feeling lucky.
avgupsvc.exe - Again, more AVG.
avgamsvr.exe - And again.
spoolsv.exe - Put these in that same category as svchost.exe and don't mess with them.
alg.exe - Windows networking process, but get rid of it if you want.
svchost.exe - Dude, seriously, don't touch!
svchost.exe - !!!
svchost.exe - !!
svchost.exe - !
svchost.exe
lsass.exe - Again, more important windows stuff.
services.exe - Same here, very important.
winlogon.exe - Also important.
csrss.exe - Same here...
smss.exe - ...and here, don't touch.
Apache.exe - Strange there're two running, I'm not familiar with Apache server, though.
nSvcAppFlt.exe - nVidia stuff, go ahead and kill once your computer is running.
Some of these need to start up when the computer starts up, but will be safe to kill once it's in booted up all the way. You should be good to close everything, once you're up and running, leaving only:
spoolsv.exe
svchost.exe (multiple, don't close any)
lsass.exe
services.exe
winlogon.exe
csrss.exe
smss.exe
explorer.exe (if you're really being stingy about RAM and opperating overhead, you can close explorer once you start doing something more intensive, but you'll lose some functionality of windows.)
Edit: You may want to get a copy of a program called HijackThis in order to prevent Apache services from starting.