I don't think so. If it's not set up as a service, it won't run under the other profile, and even when you try to run the service version and GUI version at the same time, it senses that and won't start up the one started last.
Nope, you can do both. DIMES requires little to no CPU time, it's purely networking related, pinging and tracert'ing IP addresses. I've been doing DIMES for going on 2 years now, only started folding back in April 07, with with 9PCs/10cores.
Check out the links in the DIMES info sticky, Jahara - maybe you'll want to join up!