1) change your system to 2000 pro its the starngest and the best from microsoft.
2) the anti viros isnt slowes nothing but in XP its alwes more slow then 2000-pro, me. 98 . 95 and so on beckos she using your grafic card more then thos so beckos that XP is socks.
3) yes its alwes good to set up an virtrol membory but not to mach beg beckos then the program isn't use the membory in the best why.
4) in 100$ you can upgrate your computer in alout over-clocking thats thae word you buy an colt seysitem put her on your pc/ atalon (i dont now this is with mac) and on your garfic card and then do over-cloking you can found how to do it over the net but if you are afriad then call to an pro-man that well do it for you (i on my own macke my pc from 1.6MG to 2.8MG and speed up my grafic card in abut 300% from his start) but its also stop your nasorsty at inter or what ever is your compny