newb question

well at my buddies house his internet come in on the main floor. But his sister needs inet upstairs and they dont want to run cat5 up there. I havnt done much with wireless so im just inquiring to see if it will work ok for inet, what brand and protol for the cost is best. File transfering isnt a big issue but i wana make sure connectivity is stable. Any help would be great, thanks.

wired will be cheaper and assuming they don't want the cat5 run, money isn't as big of a factor.
you can buy a wireless/wired router (acts as a wired router but also has wireless feature to it) and hook the first computer up through the standard cat5 cable, the 2nd computer can be wireless.
The downfall to using Internet Connection Sharing is that the computer that is sharing (the wired one) must be on at all times. I personally shut my computer down when not in use, but if you leave it on constantly, go for it.
My advice is to purchase either a wireless router or a wired/wireless router and hook them up. You can do both wireless with the wireless router, or 1 each way with the wired/wireless router.
Downfall to wireless? "War Driving"
In some cases people drive around and hook into unsecured wireless networks to do illegal things. Common? Not really, but it does happen. The company Lowes was the latest major company to get hit.
I would push them for the wired, but if wireless is what they want, you'll need the router, the wireless cards, possibly even an additional access point to get the connection, depending on thickness of walls and distance to the wireless router.

Riser