Yes...another hammer licensing question

I know for commercial projects, you're not supposed to use Hammer to create levels...but reading the license for Hammer seems to imply that it can only ever be used for Half-Life based games, even if you're giving your game away for free. But garagegames still has documentation/an exporter referring to the use of Hammer, which implies that it's ok to use in certain situations. So what gives?

For the record, I'm doing a game for a school project (that will be given out for free), and in my experience, Quark isn't quite as intuitive as Hammer is (aside from the whole "textures must be in a .wad" thing). Sorry for possibly bringing up a dead horse, but I seem to be hearing conflicting reports.