Cable and Internet connection help

First, there is no point in running cable down to the basement unless you want TV down there (for internet you would need another cable modem if you did it that way)
Even if you do want TV in the basement, your best bet is having a wireless capable modem or router upstairs and a USB network adapter on your computer, or better yet run a new network cable down there.
Hard wired is ALWAYS better I don't care what anybody says.

If you look around a little on the net you can get wireless USB network adapters pretty dang cheap these days.
I have one that is N wireless USB that has a reliable range of about 150 feet that is so small it is almost not noticable (looks like a wireless mouse chip) that I carry when working in case I need to add wireless to anything.

This one is a little bigger than mine and is 300N capable and look at the price.
[ame="http://www.ebay.com/itm/300Mbps-Mini-Wireless-USB-Wifi-Adapter-LAN-Antenna-Network-Adapter-802-11n-g-b/300992969685?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D24903%26meid%3D1a4e0b4f5b0642709678f4cfbe57f456%26pid%3D100033%26prg%3D10502%26rk%3D1%26rkt%3D4%26sd%3D300992969685#ht_1607wt_983"]http://www.ebay.com/itm/300Mbps-Mini-Wireless-USB-Wifi-Adapter-LAN-Antenna-Network-Adapter-802-11n-g-b/300992969685?_trksid=p2045573.c100033.m2042&_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D24903%26meid%3D1a4e0b4f5b0642709678f4cfbe57f456%26pid%3D100033%26prg%3D10502%26rk%3D1%26rkt%3D4%26sd%3D300992969685#ht_1607wt_983[/ame]