There are a couple of things to watch out for.
First, Eraser may not be able to clear cluster tips (unused space at the ends of files) if the files that occupy them, such as NTUSER.DAT (registry files) are locked.
Second, be sure you've actually deleted the information. Windows, and other programs, create all sorts of extra temp files and other records that may indicate what files were deleted and even give away the contents of the files.
To deal with the first problem, it may be wise to run freespace wipes under more than one user name, as well as at startup or shutdown before certain user files can be locked.
It's also wise to run freespace wipes both before and after defragmenting the disk. Certain programs, such as Page Defragmenter (freeware from http://www.sysinternals.com/Utilities/PageDefrag.html
) will allow you to defragment system files, too.
To deal with the second, there are a number of excellent free programs that can wipe the "usage tracks" Windows creates. One of the best known is Spybot S&D (also free):
Another is MRUBlaster:
which eliminates "most recently used" lists on your computer. There is, of course, some overlap between the two.
A couple of other tips:
If you run email software that downloads your emails to disk, deleting email doesn't necessarily delete the text of emails. You'll want to empty trash and "compact" or "compress" mailboxes.
Also, Microsoft Office documents store a tremendous amount of tracking information in documents. Even law offices and government agencies have gotten in trouble for leaving this information in documents. Microsoft has information and tools for eliminating this data:
http://msdn.microsoft.com/library/defau ... ctWord.asp
By the way, if I were you, I'd run useage track elimination software before
running a freespace wipe.