Hi BP

,
Errrm, how shall I put this?
Linux is most surely not the only way to go.
Even because BSD is au pair with Linux.
Plus, the nicest VPN projects are using BSD and *not* Linux.
Remember me mentioning m0n0wall and pfSense?
M0n0wall is a state-of-the-art router/firewall/vpnserver/Host AccessPoint/etc... booting and running off a 16MByte CF Card

.
I'll tell you, this baby rocks!
And you can configure it via HTTP or HTTPS(secured) sessions with it's wonderfull GUI

.
pfSense is still in Alpha stage but it will reach Beta and RC in a few weeks.
pfSense promisses to be the next step to m0n0wall users even because installation has been much improoved when compared with m0n0wall.
Now try to do all this with M$ Windows...

Of course W2K and the ipig server might do the job but just remember that M$ is about to move W2K to the legacy products thus stoping the maintenance updates (or at least not distributing them as regularly as with W2K3).
So I think you should consider W2K3 if you test it with W2K and you like it.
Oh, did I mention that m0n0wall and pfSense can be installed on a generic desktop PC with no need for a Soekris/WRAP SBC?
You could try it on that same PC that you'll use for ipig

.
Cheers BP