I've used Windows 7 under bootcamp (not VMware) and used a 16GB partition. If I turn off restore points, then I get about 4GB free. You should be able to do the same thing with VMware.
He was lying. Windows 7 takes up 2.4 GB as an .iso image in 32-bit and 3.2 GB as in .iso image in 64-bit.
However, once all files are expanded and installed, the total space required is ~ 16 GB give or take. 20 GB partition should be enough if you only plan to use your Windows partition for testing purposes, but if you plan to game a little, I'd say use 25 GB, gives more breathing room for games.