I just finished installing a Windows 7 Pro upgrade from Vista. I now have almost no room left on my hard drive, which used to have about 100+ GBs free. What can I safely delete?
It seems you did an "in place upgrade" install, keeping a lot of stuff from Vista, instead of doing a clean install.
You could try to clean it up, for example if it kept some files in C:\Windows.old. You can delete a lot of what's in there and only keep any personal documents, pictures, etc.
Doing it that way, you will need to reinstall all your programs in the new OS, but you won't be wasting space with old files from Vista, which are difficult to find, or to know what can be safely deleted. Also a clean install is more reliable than an "in place upgrade" which is what I guess you have done.