Remote Desktop w/UltraVNC and NAT device

I recently got DSL and wanted to remote into my computers using
UltraVNC. The problem is that my provider (Earthlink/Sprint) has given
me a modem (zyXEL 660 series) which is also a NAT Router (their words
not mine). Because of this I am having a heckuva a time getting my
wireless router to forward the ports.

Here's the setup: Internet --> DSL Modem --> D-Link Router (DI-524)
--> Computers on LAN

I have read that it might not be possible to forward ports and whatnot
becasue of the nature of NAT. I know there are alternatives like
Hamachi and OpenVPN, but I was hoping to only have to use the VNC
client. If anyone has any ideas I'd really love to hear them.