You connect to your buildings T1 line via a RJ45 port correct?
If yes then from your wall to a Wireless Router's WAN port connect the two with a standard network patch cord.
A Wireless Router is a router and a WAP. The router part will block off your network from your building network which is what you really should have and the price is not that much more. The router part is often refered to as a hardware firewall!
Most wireless routers also have 4 hard wired ports or switch that you can use for a computer that is close to the router.
In the routers settings you can assign you WAN (outside)IP Address manually if you know what it is or you can set it to obtain it from the DHCP server. (there prob. is a DHCP sercver running in your building)
Then of course you will want to lock down your wireless setting unless you want to share it with the world
Linksys or netgear would be my first two choices then D-Link... but any should do the job just fine.
Hope that helps