where does malware live? how to customize antivirus scan?

I I recently had a slow computer. I use Win xp pro and have 160 meg hard drive. I suspected bad stuff so I ran my antivirus. But it took more than two days to finish. Is this a common problem now with large hard drives? Therefore, i wonder how should I customize the scan to check those parts of the PC that are most probably infected. I would like to get the scan down to less than 7 hours so I could do it overnight. Thanks Frank

 

Windows directory "C:\Windows"

Your home directory "C:\Documents and settings\USER_NAME"

 

It should not take 2 days to scan a 160gb disk, which I assume you mean.
You should clean up your registry, clean up your hard disk, and also use a varient of Mozilla, rather than Internet Explorer .