When hard drive free space gets below 40% it will slow down significantly as your free space gets smaller. Remove any unused programs and games. Run Windoze 'Disk Cleanup' and clear out cache and temp files. Backup and remove that five years worth of emails, old photos, mp3's, etc.
Download and run AdAware & Spybot Search and Destroy.
Run defrag. Run Defrag again (LOL) - the Windoze defragger is kinda crappy. Read the report upon completion and check for page file fragments. (If you have more than a handfull of page file fragments download VernDewds Page File Defragger from M$ and run it.)
Download a copy of
HijackThis! and post your log to this thread so we can see what's going on with your rig.
With the amount of money you are planning on spending on your new rig you should definately hold back $300 to upgrade your current rig.
You need more RAM. Check and see if you mobo is capable of dual channel. If so, buy at least a 1Gb kit. If not, at a minimum increase your memory another 512mb - RAM has gotten really cheap these days.
If your video card is the X850 Pro you should probably upgrade that pos. The X850 XT was 20% faster and the X850 XT PE was 30% faster than the 850 Pro. Consider something like the
Radeon X1950 XT 256MB 256-bit GDDR3 AGP 4X/8X for around $140 - easily twice as fast as the 850 Pro.
If you mobo has SATA capabilty (or even if it doesn't) hard drives are really cheap ($.25.Gb) these days. Run your OS and apps on your original hard drive. Setup a shortcut on your desktop to the new hard drive and store all of your *files* on it.
Design a directory/subdirectory *tree* on your storage drive that reflects what you do, i.e., set up folders / subfolders for CAD, Computer, Downloads, Graphics, HTML, Office, Politics, Rips, School, Videos, etc, and keep your stuff organized. If the OS/Apps hard drive crashes you can easily move the drive to your new gaming rig and not miss a beat.
That processor you selected for you new rig is a waste of money (insert flaming here >___< ). You will be able to purchase a e6750 @ 2.66GHz 1333 fsb for $183 on July 22.
Post that HijackThis! log and we will make suggestions to speed yah up . . . .