is there a free space wiping utility that works with vista?

Yes. You have several options availible:

nCleaner (http://www.nkprod.ro/ncleaner/)
-will shred free space to get rid of files you may have deleted before
getting the shredder
-will get rid of tracks that alot of software leaves
-and it's free! (as long as you are not using it for commercial purposes)

File Shredder (my, what a creative name http://www.fileshredder.org/)
-will do everything that nCleaner does except getting rid of tracks but has
a slightly unappealing interface
-has five different levels of wiping

There are many different options, but these two are my favorite. If you want
anything else try going to http://www.freewarefiles.com and searching for
shredder