For sure the g: can hold 137GB, and the f: can hold around 297GB. If you go over your 297 mark on the f: partition, you could corrupt your HD and will have to reformat it. This has happened to MANY people! So I guess to answer your question it is just over 400GB...
I wouldn't want to see the speed it would navigate when it was full....hehe. A full 200 gigger is slow enough for me.