that the client will run on a single core if you don't add the -smp flag. It's basically similar to the Linux client in operation.Edit
: The best temporary solution, though, is probably the same as one I found for my GPU client to run on XP Pro, which is a utility to modify priority. For someone only running the SMP client, he can probably just change it manually and leave it be until it downloads the next WU and he wants to use it for something else again. Or a script could be written to lower the priority every, say, 10 minutes, and that way he'd never find it troublesome when he began using it unless it happened that he got there right at the start of a new WU which hadn't had its priority lowered yet, in which case he could just run the script itself that is called by crontab and that would be that.