hmm thats odd, never happened to me, is it when you start the terminal from within xfce or did you not get that far as to install it yet?
If the regular mint is such a strain on you computer that you cant start the terminal it would probably not work with Mint Xfce either.
You could try the XFCE Community Edition BETA 008, works great for me on AMD Duron 1.3/256 sdram
Or howabout trying fluxbuntu? Mint is based on Ubuntu, and Fluxbuntu is Ubuntu with Fluxbox ontop, really lightweight, it is some work getting mp3, divx, encrypted DVD's to work, but under the hood it is the same thing as Mint, just a little rougher around the edges.
Fluxbox is not as pretty as Gnome though, but what can you expect, as long as you get the job done right?
Get it here:http://www.fluxbuntu.org/js.html
Get your media codecs and howto make them work here:http://medibuntu.org/