Even if you could squeeze it in (doesn't look like you can without deleting something), you don't want to fill your drive to capacity.
If this is a desktop/tower, and you have room for another SATA drive... well, HDD space is CHEAP right now. 1TB drives for $50 and such. If it's a laptop, there are 500GB-1TB drives in the same price range (about $50). Also, external USB HDDs are about 1TB for $60 right now.
If you don't want to spend any money, I would say you have to make some choices. If you can clear out some space, go for it.