adding an access point to a wired network

You have 2 options. Either replace your router with one fo the newer ones that have wireless or add a AP.

All of the wirless routers that I know of have 4 nic ports. I here people complaing that they have problems going through walls. That is mainly due to low gain (2dbi) antennas that come on routers.

I added a USR5054 AP to my system. It comes with 2 HI gain antenna (5dbi). With it I can cover my whole house on low power. The antennas along will cost you $30.00 each if you had to buy them.

If you are going to be working in the same room as the wireless router, you want have any problem.

I am able to cover my entire house with the power set on low. 5 walls in 60ft.

As for cost you pay about the same for a wireless router as you would an AP. I like them seperate, that way if you need to relocate (or raise) the ap to get better coverage you can with out moving all of your equipment.

I ran cat5e when I needed one the the bedroom. Then I got tired of the cable and added the USR 5450AP. It has been a trouble free unit. I have the PCMCI card (usr5410) to. I connect at 125mbps on the 11g. Great improvement over 54g.