Hi all. New to the forums and love the router, just can't get VPN to connect

Have tried:
- Virtual Servers (need ports 500 & 4500, UPD)
- Port Forwarding (500/4500)
- Pretty sure I've tried all combinations of the above,
plus any/all of the following checked/unchecked: SPI, PPTP, IPsec
- Resetting to defaults and starting the above all over again
What I have:
- XPSP2
- router is hardware version A3, firmware version 1.20
- PC wired to router (for now anyway -- will get brave & go wireless after I get this resolved)
- DCM-202 cable modem
Sure don't want to go the DMZ route. VPN works great if I connect the PC directly to the modem. I'm really hoping one/some of you can help me before I return this for something else (which is what my work Admin said I should do).
Thanks