VPN?

I would like to setup VPN on some Tao boxes. The VPN will be used with 
roaming Windows clients that need access to a network for file access and 
place/receive voip calls. Ideally the clients should be able to connect 
using the built-in Windows vpn client to allow vpn access even from an 
internet cafe.

Any recommendations on which VPN server to use? I noticed that the VPN 
server that is included in RHEL3 is not included in RHEL4 beta. I would 
prefer a system that can be easily migrated to RHEL as soon as it's 
released stable.

Thanks!
Remco