problem with high cpu usage, hanging etc (mid-2009 MBP)

Hi

I have a mid-2009 MBP (13" 2.53Ghz core 2 duo, 4gb ram) running 10.6.8. I have been having some trouble lately - it is getting quite a bit hotter than normal (istat tells me it its about 80 degrees near the CPU and a bit less than that in heatsink B). The fans have not been turning on (I'm not sure how hot the computer needs to get for the fans to be on - but istat tells me they're not on, and I definitely can't hear them!).

Just earlier I got this in Activity Monitor (pic attached). The computer was very slow across all applications - this picture was taken once I'd shut down word, preview etc and just had safari. I'm not sure what that kernal task is that was taking up so much power.

When I repaired disk permissions it was (when I copied the log across to word), 427 pages long!

I am also posting to here using firefox, because safari kept on hanging and couldn't type into the forum (although the slowness seems to be affecting most programs eg. word).

Does anyone have any idea what the problem could be? should I be worried or will the problem rectify itself? Any advice on what I should do? I am still in apple care warranty, and the hard drive was replaced a couple of months ago because it was failing.

Thanks