IF all your PC's are upstairs you could move your router upstairs you could have a good quality cable running from your phone socket (adsl filter) to your sky router.

You have a few options with connecting both PC to the routers, 1st could be WIFI (wireless)

or the 'Home plug' option

or an option which hasnt been mentioned in the thread is Ethernet port. The original to the first PC and buy a seperate longer one to the second PC.

The cheaper and easiet option would be the last one^ because I bought my 10 metre cable running from downstairs to up for 12 and its just a simple plug and install orignal Sky disc. The disadvantage is the wires.