You don't say who's SMTP server you want to install. In any case, I'll offer a couple of suggestions.
Sendmail is the bomb. However, it does have a rather sharp learning curve - there's a good O'Reilly book called "Sendmail" that walks you through the entire configuration. It's about 800 pages. The sendmail distribution is free and a Windows 32 bit version can be found on download.com
Be warned - most mail server packages will have all sorts of other things turned on - most notably port 110 or POP3.
There are other SMTP/POP3 applications on download.com so pick the one that best suits your needs.
Tony