[CentOS] VPN Solution required

Hi

I need a VPN solution that will work to a CentOS4 server thats behind a 
NAT'ing hardware firewall appliance. This has to be able to work on 
Windows and OSX and i have to access a server on the LAN.

I have looked at OpenVPN but for some reason i'm having issues with 
generating certificates using their howto and i used the rpm from Dag. 
While i continue my fight with this is there any other options out there?

thanks