I just did something similar, so the answer is yes.
Your existing router (or switch) needs to have one available port.
As a matter of fact I did indeed add my access point to my existing switch.
I used the Microsoft MN-820 Notebook Kit. You need to use either an actual access point or a wireless router on which you disabe the DHCP (routers cost less than access points as far as I know).
The Microsoft MN-820 ($79.00 at BB for the wireless router, wireless notebook adaptor and cat5 cable - 802.11g) has an option to use it as an access point.
DLink has a wireless kit (router + notebook adaptor) in 802.11 super G (108mbps) for about $89.00 after rebate at buy.com.