OK, here are a few general precautions to preserve your computer.

1. Get a firewall, I use ZoneAlarm, and that's fine.
2. Get a VirusScan, like McCafee VirusScan. Run it every few weeks.
3. De-Frag your computer often, every fortnight. [Start--> Settings---> Control Panel---> System Tools---> Disk Defragmenter.]

Hope it helps .