Need wireless LAN advice

[wuushew]

My friend needs to a share internet connection from the next door building.

He currently has a a wireless router at the internet end and a wireless access point at his end. His Macintosh lacks a wireless card and I really want to avoid opening it up and installing one. Can I simply use a CAT5 ethernet cable to connect the Mac and the WAP?

Both are Linksys wireless G devices. Surely I don't need a wireless bridge or another WAP? What is the fewest number of devices to accomplish what I want?