Vista system restore attempt throwing "not enough space" status

Hi!

I'm trying to restore my computer to a previous point in time (earlier today) using the "System Restore" utility. After I select my restore point and click on "Next", I'm noting in the next screen ("Confirm disks to restore") that my C: drive is showing a "not enough space" status (as opposed to the expected "Ready to Restore" status). Do I need to do something as simple as clearing out files from "temp" directories?

To complicate matters slightly: I'm unable to boot into the Windows GUI. When I power up the computer, the "Startup Repair" window stating "Your computer was unable to start" appears and attempts to correct the problem. After a few minutes, it reports that it cannot repair the computer automatically and presents me with a "System Recovery Options" window. Since the initial Startup Repair was unsuccessful, I'm choosing not to select that option again...so I thought the "System Restore" option would be the next best approach. When I try to perform the System Restore, I run into the scenario that I detailed in the first paragraph of this post.

Any help would be greatly appreciated, and I'm more than happy to post additional information as required.

Thanks!