An access point is the equivalent of a hub, it allows all machines in range to communicate with each other and with the wired network it is connected to, it wont share your internet connection and it doesnt have any wired ports.
A wireless router will share a broadband internet connection and usually has wireless ports, and is a litte more expensive. Dont get one of these and put it behind a wired router though, one router causes enough problems for games, getting two to work nicely in a chain could be difficult.
As to wireless cards, I'm afraid you made a bad assumption there. The 4780 uses a miniUSB port for its wireless and, like the 8890, doesnt have the more common miniPCI port (someone correct me if I'm wrong on this, I dont have a 4780). As yet, there are no G miniUSB cards, which is why pctorque doesnt offer one. There will be eventually, miniUSB is the future standard provided PCI Express doesnt kill it off. You can either change your order if it isnt too late, buy a miniUSB B card, or get a G PCMCIA card while you wait for the internal G. I opted for the internal B and I'm still waiting.
Edit: Sorry I assumed you wanted internal wireless until I re-read your post, you can of course pick from a load of PCMCIA cards if you dont mind the stubs. I've personally always liked netgear although linksys gets a lot of good recommendations. I dont know of any that dont work for the 4780 specifically.