I have 2 computers through Dell. One is the 4700 and it came with a wireless internet card, I bought it in 2005. In 2007 I bought the E520 and it was SUPPOSED to come with a wireless card. But DID NOT. I have spoken to a few people since last year at Dell and been told that all computers sold/made after 2005 would have wireless.
Now I am running a 25' cable from my main computer with a wired router. I want to get wireless so the E520 will work better, run faster and connect better to the internet.
I was told to get a wireless plug-in thing, like a USB into the back that is for wireless internet. I was told to get a N one for the E520. Can I get away with buying a G one instead as those are really cheap.
You misunderstood about all computers will have wireless. That only applied to notebook computers, not desktops. No desktop has wireless unless it is ordered. I doubt your 4700 came with wireless. All desktops come with an Ethernet wired card.
Sure you can get a G card. If you got an N card you would need an N router to go with it and that's expensive and then you might have problems with your old computer. Get a card that is the same brand as your wireless router. I'd get an internal card if you have a slot for it.
I noticed on this message board some members are using a Wireless game adapter. This adapter might work with your computer. It would have antenna(s) built inside the case for getting the signal to the wireless router.
This is a link to all of the adapters sold by Linksys so you can check products and prices. Mary G makes a great point. Most people buy a wireless router, and adapter from the same company. You can find most products online, and get an idea what is being sold before going to a store.