Wireless adapters are backward compatible.
Do not use a USB NIC, use an internal PCI wireless NIC.
At present I have one Dell Dimension 3100 desktop PC and a Dell Vostro 1510 laptop. I have DSL service with AT&T. I need to buy another desktop PC to replace an old WIN 95 machine but I'd like to use the DSL signal on the new desktop which I'll have set up in another part of the house. I have a Linksys wireless "g" router, my laptop has a wireless "g" card. Dell's Vostro desktop line offers only one wireless card as an option, a wireless "N" card.
Can I just pass on configuring the new Dell desktop with a wireless "N" card and instead purchase some kind of after market plug in external adapter and plug it into a USB port on the new desktop which would allow me to have access to the DSL signal in the house? If I need to configure the new desktop with Dell's "N" card will the "N" card work with my Linksys wireless "g" router which I have now or not? I don't want to have to buy a new router just for wireless "N".