You have a couple options I can think of. Sounds like the MBP and PC are going to be physically close to one another, close enough to be wired together.
1. Cheapest: Get an ethernet cross-over cable. Wire the PC and MBP directly together. With no configuration, they might just work. But otherwise, you can hardcode an IP address on both machines. You connect from the MBP to the PC using the IP address of the wired connection. This leaves the wireless network configuration of both machines alone. You continue to access the Internet over wireless. Downside: A little tricky to configure if you aren't a networking expert.
2. Next cheapest: Get an ethernet hub and plug the MBP and PC into the ethernet hub. Really isn't any different than option 1 except you can plug more things in on the wired side.
3. Get a 802.11n access point and a hub. Plug the AP and computers into the hub. Configure the AP to join the 802.11 network in "bridge" mode. Just about any AP should be able to do that. Possibly a little cheaper than option 4.
4. Get a 802.11n router with a built-in hub. An example of this would be the AirPort Extreme. 802.11n wireless plus USB port (to serve disks or printers) plus 3-port ethernet hub all-in-one. Plug the computers into the ports not marked "WAN". Leave the WAN port unused. Again, you'd configure the APE in bridge mode. This is the "easiest" because it's just one box that does everything you want. Other vendors have similar boxes as well.
For options 3 and 4 you'd turn off wireless on the PC and MBP altogether and only use the wired link.
