The actual campaign setting book uses d20, and I believe the Player's Guide does as well (it appears that you can get it free at DriveThruRPG). I didn't find the Player's Guide to be as interesting as the actual campaign setting book, though, perhaps because it's missing most of the adventure hooks (it also lacks the "Largrymm's Doom" spell, which allows the caster to make people's heads explode).

I found it interesting enough that I bought the campaign setting, though, so maybe it's a better deal than I make it out to be.