I've installed Turbo once or twice, found it to be just your run of the mill distro. Nothing too special about it, it should do you just fine. There are two versions of Turbo, Workstation and Server. Depending on what you wanna do with the version you're getting, you may end up downloading additional packages. The best way to learn about distros is to just try em out for yourself.
I have a Caldera ISO that I downloaded and burned today, going to flatten my RedHat partition tomorrow and try that one out. Never used it, and don't know too much about it. It shall be my distro of the month I guess.
I happen to like RedHat for some reason. I guess it's because it was the first one I installed back in 95 or so, and I've just stuck with it. I would avoid RedHat 7.0, they've done funky stuff with the libraries and it can be tough to get things to compile. The betas that are out (Wolverine was just released a day or two ago) would be better and won't leave you fighting with problems. I've found that it is generally best to avoid the x.0 versions of RedHat, it's better to wait for x.1.
Slackware is a bear to install if you don't know what you're doing. You can really get your hands dirty when you install it.
I've only seen SuSe running, never really played with it. It's supposed to be very good, and a very thorough distro (lots of included packages).
One thing to note, if you wanna keep the data on the drive you are partitioning, I know that RedHat (possibly lots of others too) comes with a program called FIPS on the CD. It is a non-destructive partition tool ala Partition Magic -- but free. Check you favorite RedHat mirror in the dosutils directory for it, small enough to fit on a boot floppy. I know a few people that have used it with great success.