In the situation of wanting to allow just a small but steady amount of CPU time you'd be better of the often mentioned TThrottle and for the smoothest, ThreadMasterGUI [See Start Here FAQ, at bottom **]. That's a permanent fixture on my W7 Laptop. Only thing needed is to add the science application from a pick list and set the percent for that science. Try it at 25% and you'll never know it runs, except maybe at the 3rd and 16th last checkpoint. When using TMG, BOINC itself needs to be set to 100%. TMG default is 25%, meaning if the science app is not in the table, it will limit anything low level [BOINC is] to 25% CPU time. The control is on a "per science" basis.

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** Just updated to add that it runs well on Windows 7 too.