I use RH7.2/sendmail 8.11/PHP4.0/Apache1.3.22/UW-IMAP
this was a piece of cake to configure. I also added mod-ssl for encrypted web and IMAP sessions.
to install Apache and PHP go to www.webmonkey.com
type 'PHP installation' in the seach engine. Search for the tut on 'installing PHP and Apache on WIN/Non-Win systems. It's a good idea to compile Apache and PHP w/ DSO support.
If you're unfamiliar /w apache and php then you should definitely stick w/ apache 1.3.22. Apache2.0 is alittle different and there are not too many good tuts out there on it.
For the webmail part go to www.squirrelmail.org
SquirrelMail is easy to set up and configure and has lots of pluggin support.
UW-IMAP is really easy to setup, too.
The only problem is compiling it correctly to support mod-ssl. I think you use the -slx OSTYPE to get IMAPS to compile right.
-hope that helps