Mail enable is a good free mail server, the free version does everything you wish but it does not do the webmail thing!
It is a good starting place though;
MailEnable Standard Edition provides robust SMTP and POP3 services for Windows NT/2000/XP/2003 systems. Its simple installation procedure and powerful administration software means that you will be up and running quickly. This edition is FREE for both personal and commercial usage, and does not have any time or user restrictions
By the way please be careful when setting this up. I have run one for 3 years now and it provides mail to many users, however if you muck up the config and it runs as an open relay then you can find 160000 emails going through your server. I did and ended up on every black list going. Even the woman in the newspaper shop had my IP address! Luckily enough I was thick then and I read the manual which is comprehensive. A quick change of I.P address and you are away.