Config Help for Linksys Router on Existing Network, please

I'm having little, if any luck connecting a new wireless router to an
existing wired network. My existing network connection has a static IP
address of 192.168.100.117 which I had my PC connected to for quite
some time. I'd like to connect the new AP to that port and have the
added functionality of being able to use the wireless card to work
around my office.

The exact setup is where the problem lies. I'm not completely sure how
to configure it to be used in this manner. The primary Internet
Gateway IP (a DSL modem) is 192.168.100.1. I've tried various
configurations of plugging one of the 4 ports on the back of the AP
into the wired ethernet port, plugging it into the Internet port on
the AP, as well as a host of possible configurations in the router
itself with very limited success. The best I've been able to do was to
access the outside world from the wireless card, but access to the
rest of my network has been non-existent.

Can someone point me in the right direction or suggest what IPs need
to go into the LAN, WAN (Static, I presume?). Do I put the gateway IP
of the DSL modem in, and the DNS IPs of the ISP?

Any help would be greatly appreciated.