This is driving me nuts. We've got three affected Win XP SP2 machines at werk, possibly more. At some, seemingly random, time one of the two copies of rundll32.exe goes bananas and consumes all available CPU on the machine, dragging it down to a crawl. This seems to have happened on older machines, as well as fresh installs.
The requisite net-trawling suggests very little, except it may be one of three trojans. I've followed the removal instructions for all three, but found none of the affected registry keys, nor did Symantec Client Security scanner find any suspicious files (yes, we have the latest virus definitions, etc).
Windows costs you more. Just this one issue alone has already cost us a significant amount of time and developer down-time. Not good.