Ok so I had a virus on my hard drive. So I reinstalled windows on my computer and went in and deleted the old partition. My hard drive is 120 gig's and that partition was 100 gig's. now my computer says i only have a 15 gig hard drive. Is there anyway that i can recover the rest of my hard drive without losing the information that I have on my computer right now?

Some viruses can stay on a computer--even more vicious ones can stay on even after you format, delete partitions, etc. Where did you see the information that showed you how big the hard drive is? Was it through BIOS or through the installer?
Like smartmom suggested, you should probably back up the data on the other partition just in case. I've learned the hard way what happens when you make changes to something and can't go back
Did you try putting your data on a external hard drive? Did you remove the virus prior to deleting the partitions so that the other areas were not corrupted? Deleting and reinstalling your OS shouldn't have anything to do with your partitions. In fact partitioning it would even allow you to duel boot. I would try backing it up to a external (your data) or even using a online data storage service it you are worried (its a good idea to do anyways). There are some free ones out there.