The 3rd mandrake cd iso is a few packages that they couldn't get on disc's 1 and 2, plus all the source code. (last time I looked it came in slightly less than disc's 1 and 2, which are about the 650meg.s mark, and 3 was about 400 meg's).
But yes, I usually get all three, and tell the installer that I've got all three (it ask's when it's doing it's thing).
As a final suggestion, current mandrake is version 9.2, whereas version 10 is now at the RC1 stage, so it might be better to wait.
So, in the mean time, download knoppix
, burn that to disc. It's a "live CD" that runs from the disc, and won't install anything to your harddrive unless you tell it to. It's compressed, but opens out/runs nearly 1.7 gig's of software.
A good one to play with (or show your mates, you just take the disc with you). If it see's all your hardware OK, you can even install it to the hard drive, which gives you a nice easy way to get a debian based system (no mean feat, if you've ever - like me - tried to install "proper" debian), working, configured/up and running. It's got open office, for admin tasks, some games/amusements/entertainments etc, plus pretty much everything else you might want.
If you check out the knoppix, don't forget to select en or us (cant remember which it offers), because if you got the default you're screwed, unless you're a native german speaker (if you got the en flagged download, it should be in english).
That then takes the discision away. and you get to play with a linux distro, while waiting for mandrake to release version 10 final (with it's 2.6 kernel, kde 3.2, etc etc).