Slow Internet question

Hey. Me and my roommates (2 of them) have been using a NetGear WGR 614 v 7 router to connect to the internet wirelessly. I am using a desktop with a Gigabyte GN-WP01GS PCI WLAN CARD (TURBO) to pick up the signal. My roommates are using stock wireless cards in Toshiba and Dell laptops respectively. The router is about 50 feet away from the farthest computer which is the Dell laptop. My desktop is about 25 feet away from router. All of us have been experiencing difficulties with the internet saying full wireless strength, but continually running slow or telling us websites are "currently unavailable" needing to be refreshed about 8 times. Can anyone give me a decent reason why any of this is happening or any possible fixes to the problem? Oh also if it matters I have an Xbox 360 plugged into the router in the second port. Thanks in advanced!