Kool Tools: Wormhole Switch
The Wormhole Switch from J5Create (www.j5create.com) is a good tool for trading files between Macs and PCs, as well as iPads. It requires (on the Mac) OS 10.5 and higher and (on a PC) Windows 7/Vista/XP/2000.
The JUC400 Wormhole Switch -- the top-of-the-line model and the one you'll want-- provides simple plug and play file swapping and content sharing across multiple platforms, including Windows to Windows, Mac to Mac, Mac to Windows, and Mac to iPad. You can share clipboard content across the multiple devices -- all without installing software or adjusting settings.
KM functionality built in is built in so you can share a keyboard and mouse between two devices. You can use either the keyboard or mouse to control the other device.
If you're looking for a simple solution that will allow you to directly transfer files and work on multiple platforms, the j5 Create JUC400 Wormhole Switch (US$40_ is worth checking out.