First I have to ask you one question out of curiosity...
Why are you installing so many diffrent Linux distributions in VMWare and not proparly in it's own partition? dualbooting with Windows if you like. Performance should be much better.
And now onto your question.
It is never a good idea to install packages from another distribution if there are packages done for your distribution. As far as I understand Mempis is based on Debian and should have packages for GNOME.
If you have configured Mempis to get updates and software from Internet I would first try with this:
apt-get updatethen
apt-get install gnomeIf Mempis is not configured for getting software from Internet here is a guide from their homepage:
http://www.mepis.org/node/1324after that you try the above commands again...
if this did not help ask again and I'll see what I can come up with.
BTW if you want a linux distribution that is based on Debian, is easy installable and uses Gnome you should try Ubuntu
http://www.ubuntulinux.org/ you can download it or even have them send you a CD for free if you're bandwidth is low. And being based on Debian you have all the debianpackages to choose from should you decide that Ubuntu doesn't have all the software you need.
/LinuxSam
Ps. I'm a Debian user myself and wery much like it.