[CentOS] VPN Server Recomendations

Hi Guys,

I'm looking for a VPN solution that will run on CentOS.  I've used PopTop
with success but some clients have problems at hotels and other firewalled
locations.

If anyone can suggest something that works well with MS 2000/XP, doesn't
require too much tweaking on the client side and is fairly resiliant to
various firewall blocking, I'd be interested in hearing about it.

Shawn