Any computer can Fold and be productive at the same time - within the Folding client (both thin and fat) is the ability to adjust the amount of CPU resource that FAH uses. In my case, I have the client set at 100% on my download box (Acer AM 1610 - Vista Basic x32, Seagare 2TB, please don't laugh - it was free); when I need to do anything, I just shut off the FAH client, do what I have to do, and resume it when I leave. Since that computer is running 24/7 it works very well. On my laptop (HP G60, Intel 510, Win8 Pro), I have it running at 70% and I don't ever notice any lack of resource. Keeping in mind, I'm not a gamer, I just like to watch movies and TV shows and surf the Web, though I don't see how the FAH client can affect your system when it's off. The only thing I recommend is to keep the Graphic OFF as it's just a useless resource-hog.
Hope that helps!