close any useless processes in the task manager(crtl+alt+del). For example spoolsv.exe i'm pretty sure is your printer driver and as long as you don't use your printer before you restart your computer you should be find for closing it(Although
DO NOT SHUT DOWN ANY svchost.exe
OR explorer.exe)! Also don't use unnecessary programs while playing SRO like x-fire, or maybe TS2/Ventrilo.
If you want you can also shut down some start up processes. Go to Start Menu < Run < msconfig < startup tab, and shut down any programs you don't want your computer to load went it boots up. For ex. MSN Messenger.
Heres something else very useless to terminate lag. Go to Control Panel < System < Advanced tab < Performance Setting < Visual Effects, check off the "Adjust for best performance" option (yes this will change quiet a lot of things to do with your desktop). Now you can go to the next tab over "Advanced tab" and at the bottom you will see "Virtual Memory" and depending on your RAM you can adjust it. I have 1gb of RAM, so it recommends for me to put it at 1500mb, but i doubled mine to around 3000mb. you can try that but it will overflow into one of your drivers from my understanding if you do double the recommended.
Now i know this is a lot to take in right now but if you need anymore help just post again

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