Your RAM is at the minimum needed to install and run xfce. Don't get me wrong, you should be able to run xfce just fine, but if you could get some more RAM and bring it up to 1 Gig, you would be sitting pretty for years to come. I think KDE would run a bit slow on that machine. LXDE would run quicker than Xfce, but I find LXDE is not as polished as Xfce (I think Xfce strikes a good balance between providing a good user experience and not being too heavy).
Mint is derived from Ubuntu. The Mint developers take Ubuntu, strip away a bunch of stuff they don't want, like Unity, add in a bunch of generally available and custom developed stuff, like the different desktop environments, more utilities, multimedia support (mp3 playback etc) and create the Mint iso's. Ubuntu would not be a good candidate for that laptop, but Xubuntu, the Xfce version of Ubuntu, would be a candidate. However, for my personal preferences, Mint Xfce starts off much closer to my ideal system than Xubuntu. If I were to install Xubuntu, by the time I finished tweaking it, it would look a lot like Mint Xfce, so I just start with Mint. In fact I was on the verge of installing Xubuntu on my primary computer when the Release Candidate of Mint Xfce came out, and I sang a song of joy and shelved my plans for Xubuntu.
The optimist proclaims that we live in the best of all possible worlds; and the pessimist fears this is true