Make sure you use a firewall mate. Zone Alarm is good plus it's free. also get ad-aware, it gets rid of those spy programs that slow down your computer. Finally, use mozilla firefox instead of IE, it's quicker and has it's own built in ad blocker. I assume you have anti-virus. Make sure you do a check on your start-up memory, a lot of trojans hide them selves there. You might look at getting a uninstaller program also. This will firmly delete any of those casino jobies that stick on your hard drive.
Viruses are a pain, hope your up & running soon.