I installed Mandreake the other day, and went with the defaults except for adding the games. It did not include GNOME. I have found that by going to system-system configuration in KDE you will find the software management. I actually figured out how to install a downloaded RPM from there. I tried a couple of things today. First I went there and searched for Mplayer, found it and tried to install it. It said it had a bunch of dependencies, and I took that to mean it was going to install them with it. It asked for my CD1, I put it in, and it spit it out and asked for it again? I did some more looking around are am thinking I don't have everything on the CD I should. I then went to install GNOME, which I am pretty sure is on the CDs, and again it keeps spitting out my CDs.
It seems I should be able to install GNOME fairly easily from there. I will also check my CDs, but I really don't think it is that. I am curious to know what would happen if you try this, but as it didn't work for me I can't really recomend it.
Sorry this didn't really help you out, but I am jumping on to see where it goes as well.