I'm not sure if that would work. Are you using dial-up with the computer in your sig? If yes, just let the dial up connection handle the downloads/uploads. It will take awhile, but would be much easier than transferring "work" files back and forth.
Yes, you can. I started running both clients earlier this week and haven't had any problems. Since the GPU client uses a portion of your CPU, the SMP client is much slower. I've noticed a 500 point reduction in my PPD (Points Per Day) average; however, WUs (Worker Units) completed have tripled. I'm still unclear on whether it's better to use both clients, or stick with the SMP.
^ Some of that may not make sense.

After you run F@H for awhile, you'll know what I mean.