In addition:
Win2000 has no firewall, so as soon as you connect to the internet, you are going to get attacked. Within a few minute, your computer will be pwned!
On top of that, MS no longer provides updates for Win2000, surfing with IE is going to leave you open to attack if you stray onto the wrong website. Within a few minutes, yep, you guessed it, your computer will be pwned!
Get a good free firewall like Zone Alarm and learn how to set it up, get an alternative browser like Firefox or Opera, then format again. Install avast!, Zone Alarm and the browser of your choice and maybe this time you'll survive a little longer!
It would also help if you update Win2000 with all the secuirty fixes.
Make sure the first site you visit is Microsoft Update. Download all critical updates.
Here's a good link to help you set up Zone Alarm:
http://www.zonelabs.com/store/content/support/zasc/gettingStarted.jsp?anchor=alerts&lid=zasupp_u