Two Routers on the same telephone line

[ifwecouldjust......]

I have a spare router which I want to put upstairs (attached to a telephone line which is in the bedroom) to boost the signal and connect a skybox to. I understand this can be done (i dont need to access any other of the computers on the same network) because the second router can be set to a different IP address.

Any one done this? if so can you let me have (in idiots guide) how to.

cheers