Eh if you don't need the 8gb and are looking to make the 120gb your new main hdd, just backup an image of the 8gb and load the image to the new 120gb drive.... it'll work fine.
Ever heard of "imaging" computers? Yeah.
On a side note, doing a fresh OS install would be beneficial to a certain degree, not because of any fault with imaging, but because Windows installations become sloppy over time to put it bluntly. Also, if there's a chance that there is any spyware/viruses/etc on your old one... then just do a fresh setup.
waaaaaaaaait i just read what you meant haha... Thoughts organized now (more or less):
Maybe I'm wrong but I don't think you guys understand... I think he is saying that the 8gb hdd is his boot harddrive, and that the 120gb hdd was added later and contains programs, games, etc. So "reinstalling" would mean installing windows on the 120g drive... on top of his data. This would be disgusting to say the least.... (there are ways around this but all of it would be a waste of time in comparison to what I will explain next) so moving on:
There are programs that can shrink partitions. So you could shrink the partition on the 120gb drive to make room for the 8gb of data. You will then effectively still have both drives, but on one HDD. but the same would apply, image your 8gb drive over to the new partition you made (make it like a 9 or 10gb partition). Just make sure that your new partition has the same drive letter as your old hdd.
I've been pretty vague, but that was on purpose... this is a good jumping off point for a good ol' "google it" session.
If you need help with something more specific, just ask
<insert windows sound "tada">
