Mint 3.1 is no longer supported. This means no updates, little or no access to repositories for addition of new programs and lack of compatibility with newer versions.
With the system specs you provided, I would suggest obtaining a copy of Mint 6 XFCE or Mint 6 Fluxbox. Either will install and fun admirably on your system. (Mint 7 XFCE should be available within the next 2-3 weeks)
If you want long term support. go with Mint 5. It is the current long term support version.
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