I am by no means a network geek, and I have had no trouble getting my MacBook to talk to any Wintel that comes into the house. When my old PC died, I successfully backed up 850GB of files vial ethernet from the semi-functional WinXP box to my Mac to an external LaCie drive.
The value of a Mac Pro is not just its power, but its expandability and lifespan. It's easy to get 5+ years of service out of a Mac Pro, even if you run demanding tasks on it every day.
Obviously, a Mac Pro isn't going to be a help when you're mobile. See if you can run the apps you want on your MacBook, and replace it with an MBP when you need/can afford to.