I was wondering if Eraser frees up hard disk space, because I only have 1.22GB left of hard drive. I plan on deleting a bunch of things through Eraser, but I'm not sure if it will free up my hard disk space aswell.
The space is freed up, just as if you had deleted the files. The difference is that, if you erase the files, they will not be recoverable.
I suggest that you start erasing in fairly small batches. Windows can make life difficult if you try to run large file operations with limited free hard disk space. Also, your drive may well be quite fragmented, so you may wish to consider defragmenting it when you have completed the erasing process.