I'm using standard F@H clients. Each one crunches away on it's own work-unit. When you have a Core2Duo machine, you have 2 CPU's. When only one F@H proces is running, load will be 50% overall, because one F@H proces only uses one CPU at the time. This can easily be seen with Taskmanager in Windows. It will show each F@H proces using just under 50%. On Linux with one proces running your load-average will go just above 1 (on an otherwise lightly loaded machine), and with 2 processes to just over 2. The command "top" will show each Fah_Core proces using just under 100% (of one CPU).
I am not using the SMP F@H client, or not in SMP mode anyway. On Windows, you need to use the console clients to be able to start 2 processes. Or at least 1 console and 1 graphical I think. Both need their own directory. The first time, you need to start the second proces with -configonly, and give it machineid 2 or something, then really start it (as a windows service). Maybe you need to manually edit the machine=2 in the client,.cfg after the -configonly. I don't remember exactly. It is in the F@H FAQs somewhere. Maybe the old version 5 FAQs as SMP was not available with version 5. This is when I started folding (back in 2007 I think). I started using 2 processes: 1 per core, and I simply have not gone to SMP, although I have started using version 6. I just kept the old setup I used with version 5.
On Linux I have created 2 users: folding and folding2, with different homedirs. And installed the binaries in each I also have 2 stop/start-scripts to be placed in /etc/init.d/. I cannot upload them, but can sent them with PM for anybody interested.