Any chance of posting the specs of the PC you're intending to use, Kuragari? However, like others have said, if it's an old PC you might not get the full eye candy-ness of the latest and greatest versions of KDE and Gnome.
To answer your questions about which distro to use, I'd say try a lot of them until you find one you feel comfortable using. Ubuntu or any of the other flavours from the Ubuntu camp (Kubuntu, edubuntu, etc...) might float your boat, otherwise you might not get on with it.
One of the many great thigns about Linux, though, is that you're not restricted to how someone in some company has determined you should use the OS. If you don't get along with Ubuntu, switch to one of the others. Personally, it didn't do it for me. I do like Debian however, although ironically Ubuntu is based on Debian... go figure
I also liked Mandriva (although it was still called Mandrake at the time) when I was first starting out with Linux. I tried Suse which was OK, but I preferred Mandrake. At work I've been using RedHat (the home user version is called Fedora if you want to give that a try). I've also been playing around with a fairly new distro called Kanotix, which is kinda like the Knoppix LiveCD distro, but has fantastic support for hardware.
DVS is absolutely correct - 10 different Linux users will recommend 10 different distros. If bandwidth isn't an issue for you, and you've got a few spare DVDs or CDs you can use, then try one till you're happy with it.
Lastly, in terms of blatting Win98... yep, you can do that. During the installation of Linux, it will search the hard drive and find Windows is installed already. It will then ask you if you want to keep Windows and install Linux alongside, what is referred to as dual-booting, or if you are happy with just ditching Windows completely, reformatting the hard drive in the process, and only having Linux on the PC. The choice is yours, but if you're low on disk space, and you've got no use for Win98 on that PC, then I'd suggest you consider ditching Windows completely - especially if you have access to another PC in case you need to access the Web and your Linux machine isn't working correctly.
Hope that helps
