[wplug] Question for VPN setup

[Benjamin Slavin]

I recently had a client ask about the setup of a VPN to allow remote 
users to login to a corporate network while they are out of town. The 
requirements are that the end users will be running Windows XP (or 2000, 
in a few cases) and that they have to be able to connect over the internet.

I've done a good bit of searching around, and find myself more confused 
than informed.

Can anyone suggest a GOOD [secure] way to implement the VPN described above?

I'd like to make use of an OpenBSD server already acting as the 
firewall, but the documentation for IPSec is poor (and has actually been 
removed from the FAQ due to lack of maintenance).

 From what I've read, I assume that IPSEC with x509 keys is the way to 
go, but I'm open to any and all suggestions.

Thanks,
  --Ben