Anywoo, I only have a total of 140 gigs on my system yesterday [July 12] I had a total of 118 gigs. All of which included my software, games, pics, etc. Today when I booted up my system my pc stated I had a whooping 5.7 gigs left!
Guys...100+ gigs don't vanish overnight....I think Philly is right, the space might still be there, and he might not be able to see it because of some virus/trojan/malware.
It might not be the recycle bin, seeing that the Recycle Bin takes up around 10% of the whole drive most of the time, nor the TEMP folder, because it'd take a whole lot longer to fill up the TEMP folder with so many gigs.
I agree with Salku, do a scan.
You might also want to try an antivirus [and seeing that you haven't replied yet, I don't know if you've got one]
If you have one,
use it. Do a full system scan, without leaving anything out.
If, because of some terribly valid reason you don't have an antivirus, try
AVG, which is free for personal use.
Still, try
Ccleaner [I wonder why nobody referred this excellent app before

], it's supposed to be very effective at cleaning the right places.
As an afterthought:
I'm currently running Vista Home Basic
This
might be your problem.
[Just kidding]