Optimal Environment for Cleaning Data Removed from an Infected Installation?

Here's the scenario:
I am backing up somebody's data onto a usb drive or external hard-drive from an infected installation of Windows. To disinfect it, you have to connect it to a PC, which can expose the PC to further infection (Of course, Never, ever, ever your own machine. I treat mine as if I would a server).

My question is:
What is the best method for this? Sure you can reload Windows on the machine, get the security going on it (per the guide), run updates and all, and then throw that infected data right on in, but is this the smartest option? I'd rather get those infections off before getting it back on the machine so you don't waste time reloading Windows if something got through. I would think you'd want to have a workstation that's a reliable virus and malware killer? And on this workstation, is there a good sandbox environment that could assist in this? Maybe I'm overlooking something easier, maybe I'm not.

This would be good to know... I would like to see a guide created or help start one if there's reason. I didn't see any other posts, just somewhere in the guide it mentioned cleaning the data before putting it back on the machine. It's like a potential step "b" to steps "a" and "c".