Every single time I try to install something I got from this website the files are either corrupted or I get an error telling my 300GB free space isn't enough to install a 1.6GB game.
Do any of you have any tips for me?

um, i know it barks at you if ur main harddirve has less space than the requirements but u can go into the options or settings (i forget what its called) and choose where to install from there, if not i spose it might be a bug or summin....

Theres a bug with older installers which can only work with numbers up to 4Gb. If you have 4.1Gb free, then the installer sees only the .1Gb. Adjust your free space so that its not close to a multiple of 4Gb and try again.

How am I suppose to "adjust my free space"? Fill my hard drive with 300GB of pointless stuff? I think not, I'd rather have the problem solved.

Yes, thats what I did.

Either delete something, or make a duplicate of a large file, so that your free space is not close to a multiple of 4Gb. And, yes, Id rather see the problem fixed as well, but at least its possible to work around it in the meantime.