ok my friend is on a wireless home network with cable and one of his computers always has low signal strength or shuts off. Is there a way to improve the signal strength?Or does he have to buy a better netgear card or something. If so how much do good netgear cards cost.

personally i told him he should just get an ethernet connection and scrap the wireless but his parents don't want to have to run the wires.

The only way i know how to do it is to put Boosters near the Wifi to Boost the signal.
Ofcourse you could also use the Powerlines and put the network through there, No new Cables but a bit expensive!!!

Netgear do this and you can search on Google for Zeus Powerline Bridge.

Powerlines have some very serious limitations making them almost useless in this sort of situation. What?.. you ask. They must be located on the same electrical circuit. Just ask Belkin technical support, oh yeah, it's nowhere in the documentation. :( Point is the technology is distance challanged. A far better solution I've found is Ethernet over phoneline. Some things your friend could try though, possibly locate the wireless router in a different spot. Try changing the frequency it is broadcasting on. Some things in the house, and out of it, can affect one frequency more than another. One thing I've done for some of my customers with big houses is put a Router on one end of the house then run ethernet over phone to the other end and put another router there. Works well and they end up with wireless everywhere.