Hello everybody !
I'm also definitely interested in a firmware that supports pptp passthrough. My ISP offers VPN. So it's very disappointing that i can't use it.
Port forwarding/Virtual Server on TCP Port 1723 is only half the solution as i've read... the other half is Protocol 47 (GRE) which is elementary needed, but not supported by the original asus wl-320ge firmware v.1.9.7.8 by now.
As above mentioned the firmware source is open/available... even when i don't know what to do...
Maybe a programmer with the same interests will begin modifing... i hope so.
Best regards.