routers

connect an accespoint to the router and plug in a wifi card/usb dongle to the firewall pc..

easiest way i can think of

i think he ment he needed help how to set up a wireless connection between his router and firewall pc

Its only a T1, not much bandwidth to begin with so wireless sure wont hurt it

The most transparent way to do it would be to get two wireless accesspoints, bridge them, and put crossovercables from one accesspoint to the router's lan interface and the other accesspoint to the firewall pc's lan interface.

That would physically remove the wire between the router and firewall pc without having to change any settings on either of them.
You could probably even use an 802.11b bridge without bandwidth loss but 802.11g is more common now so you might as well use that.

Then you could make the accesspoint on the router side just a regular accesspoint (might want to use a router instead to get dhcp, unless you want to use statics). Then get something like the Buffalo WLA2-G54C to repeat the wireless signal to the lan port of the firewall pc. Might as well get the Buffalo WLA2-G54L to be the router/ap for the router side in that case...

Transparent wireless between the router and firewall pc with wireless internet access inbetween.

I have those two buffalo components wirelessly bridging two sites at work and they work wonderfully. I get a little over 3mb/s solid through it and there are at least 50 computers connecting to our main network over it. Havent had to reset it once sofar.