What OS are you running?
You can install an SMTP server with Win2000. Throw your CD in and click on Add-on Components or something like that. i think it's located under IIS.. maybe networking services.. I think WinXP supports this, too.
If, by some far-off chance you're running a *nix box, just go to freshmeat.net or sourceforge.net and search there. All sorts of stuff..