As for Kerio 2.l.5
Shane is right cant be used, but I did for years on Win Me but hast
been updated since Oct.06 and now its V. 4.x from Sunbelt and 3
months trial.

No, it *can* be used. I've been running 2.1.5 - with Windows Firewall
enabled - in XP since pre-SP1. I have it running right now in SP3, with
Windows Firewall and a router with hardware firewall. Once upon a time - and
before the router, not that the router is a drain - this was with a measly
256MB RAM, without performance issues.

The Sunbelt continuation of Kerio PF is still free, it just runs in full
mode for however long (3 months?), after which if you don't want the extras
it continues in basic mode. I doubt it would be as compatible with Windows
Firewall as 2.1.5 is, so I would turn the latter off were I running it. And
I would be running it were it not for I only need one for monitoring
outboound traffic - and you can't get much less obtrusive than 2.1.5 (as you
doubtless know!).

I also use it - or variations thereof (2.1.4 - and the Tiny version) in
virtual machines that are themselves behind the router and running on XP
running 2.1.5 and WF!

Shane