hello and thx for the help....if any one even sees this lol

when ever i play SSE it starts out ok, then it slows down. so i try to speed it up by clicking the increase speed buttons. thats when i have problems. it starts running like i dont have enought memroy..and i realy do.  i have: core 2 quad, 4 gigs mem, evga gtx 260 vid card, 1.6 tb HD's, windows vista ult 64 bit. so my system is not slow. only when i play SSE dose it slow down. and i dont have any thing running in the back ground eather. all i have going when i play is norton 360, ad-awere and windows sidebar. so can any one tell me whats going on ?  thanks.