A couple of alternatives to the long cables-
As you have a wireless router (and laptop), why not get a couple more wireless cards? (PCI cards would be better is you are happy opening up the PC's, other wise USB Wireless dongles)
Or, at a higher cost, you could use
homeplug adapters - these plug into a mains socket near the PC's & router and then you just need a short cable from the homeplug to PC/router.