pc running real slow

hi there, just thought i would ask for some help as for a while now my pc is running very slow, i have checked for spyware etc and all seems clean. i am running an athlon 3.4gh 939pin (i think thats the right one.. not the 700 one anyway) asus motherboard, 1 gig crucial memory, xp sp2 (all updated) now i used to click on a programme, say unreal tournament, it would flicker quickly and be loaded, now it sits there and sits and sits for about 20 seconds before it loads.] msn messeger is the same when i try to log but that hovers for so long that its like it has froze. i was looking at removing several programmes from the start up menu but havent got a clue which ones are needed safe to remove etc. please advise thanks

Startup processes list
http://castlecops.com/StartupList.html.
Startup manager (freeware)
http://mlin.net/StartupCPL.shtml
Uninstall programs that u dont need, do some general cleaning up, you can download CCleaner or use the Disk cleanup tool in XP and then check your disk for errors and finally defragment the HDD.