If you have a virus that resides in your BIOS then changing the harddrive will be ineffective, however most virii don't access the BIOS (only a few do), I'd just suggest a format, it should be 90-95% effective, if not a lil more.

I'd also recommend you check out this recent tutorial.
http://www.antionline.com/showthread...hreadid=244895

[EDIT]
I would also suggest you delete one of your two posts... as posting the same question twice in two seperate threads in not advisable.... it's a great way however to get yourself negged.
[/EDIT]