I have three main computers in my office; a dual-processor G5 desktop (my main machine for writing, etc.), a G4 PowerBook (for e-mail, calendar and travel), and a HP Tablet PC (for note taking and in-car GPS mapping).
Since my e-mail and calendar reside on my PowerBook, I use VNC software (short for Virtual Network Computing) on my desktop machine to control my PowerBook. The PowerBook shows up as another window on my desktop and when it’s the front most application, my keyboard and mouse control that machine. The software I use is called Chicken of the VNC. If you’d like to use a similar setup, then visit www.versiontracker.com and search for VNC to see your options.