not to be a punk.. first thing to do is remove all system processes that are none essential... If you're using windows 9x/me goto start/run/ then type in msconfig, goto startup, and un check all that you don't need.. you need Explore and Systray, all else are optional to functunality of some of your devices.... i.e. powerprofile (saves user info).. clear your temp files.. and clear your desktop of the icons.. yes windows uses ram to display the desktop, it will slow your computer down to have to many icons on the desktop... had a 3% system resource free up from clearing my desktop... and well the most obvious option buy a new computer... If you have an older computer might mean an older mother board which means some of the new video cards won't be working at their full potential because your board won't be able to take advantage of them, aswell as the new types of ram... Upgrading drivers is another thing you could do...
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Could get a half decent system with little headaches from Dell, then spend some dollars to upgrade it from local stores...
Or you could fork over 3k for a system you won't need to upgrade for another few years.. Or just wait around and see where people send you to buy parts and build your own computer (a big headache to get stuff to work sometimes)
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Good luck bud,
-BM