Well I imagine you want to do something that destroys or mutilates the data after you've deleted it. Just a windows deletion, of course, looks like it's removed the data but it can still be recovered by various methods. I guess you're running XP?
There is a program included in XP (and Windows 2000, 2003) called "cipher" which will write binary 0's and 1's on the free disk space and then patterns of random numbers so it's just about impossible to recover anything from the disk after this has been done.
If you use Widows 2003, you'll need an updated version:
http://www.microsoft.com/downloads/release.asp?releaseid=30925
Documentation for the cipher program is available at : http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/cipher.mspx
Basically all you do is manually delete what you don't want on the laptop, then run cipher from the command (DOS) prompt.
Another FREE option is called "eraser" and can be found at:
http://www.heidi.ie/eraser/