This won't work for most Windows apps which alter the registry when installed.
Anyway, the original poster has to think back on what he has on his PC and what needs to be scrubbed., I have given away two PC's with plenty of applications resident, but I never kept any sensitive passwords in my browser, and even if I did, it is very easy to delete them. If he details what he uses for email and browsing, it is not a big deal to clear out the personal info.
There are a number of install codes involved with the software applications, but he is giving those away, so why care about those?
Yes, it is feasible for someone to use recovery software and retrieve files that were deleted, but that ain't going to happen with civilians.. And if that is a concern, there are ways to make it not happen. Turn off system restore first. Then use a program like Eraser from sourceforge to erase all the free space.