I HATE programs that use the C: as the temp dir for installs. If I tell it "install to D" it should use D for temp too. I know it's not wise to have a super small OS partition, but I use to find myself constantly using Partition Magic to add a lil space to it for suck ass programs like this that need temp space. Or even worse, programs that give you no choice where to install and default to C: I don't see that anymore, but a lot of damn programs use to do it.
alent1234 is right, you should email them, this is something they could easily fix, and I don't see why they wouldn't want to. Probably an oversight on the programmers part.
Wouldn't it make sense, for any proggy you install, it checks all your partitions for free space, and since it's only temp space, uses the one that has the most? or at least one that has enough. Couldn't possible be tough to implement in all install scripts, and would make Frontline Warrior's problem and anyone like him, nonexistant.