...And once again, I find myself troubled by the same issue. Apparently, the thing about having Fraps assigned to a single core had little (if anything) to do with the lag during video capture -- what was making me lag was the fact (as I stupidly discovered TODAY -- jeez, I'm a freaking techie, I'm supposed to KNOW this BY INSTINCT!!) that I was recording on the same drive where the game, the OS and everything else was running from. -_-
Solution: I connected my external HDD and set Fraps to record on it instead of the laptop HDD. Instant remedy. Just in case any of you guys have the same problem in the future. >_>