There is a type of boinc projects that take little cpu processing and that makes them run on the side because their cpu needs are not too intensive.
For example FreeHAL@Home runs perfectly as a third project on a dual core machine because it takes almost no cpu.

I have it on my boinc but unfortunately it is not stable. Because of problems in their network one has to reset the project every now and then to be able to get workunits.