How Can I Connect To Xbox Live And Computers At The Same Time?

There needs to be internet for computer use as well.
I have two internet modem boxes and have to unplug and replug internet cords to use Live. I also have a wireless router (one computer doesn’t have wireless and it is plugged directly into the router).
Is there a cheap way to have use of the computers and the Xbox at the same time while having decent internet strength?