That depends. You will be passing client traffic over as well. How many clients and what applications will they be using on the wireless?
Depending whether or not your 1242 ap has both b/g and a radios, it could be a lot of traffic. the 1242 has a 100Mbps Ethernet interface to connect to the infrastructure, so theoretically, that would be your max expected bandwidth, with actual throughput being a bit lower.
