Assuming you're using the stock fan and heatsink the RPM changes are normal depending on load, you can try making sure your heatsink is fully sitted on the board as if it's slightly off it could lead the sensor into not adjusting fan speed properly. Also, software temp monitors tend to be fairly inaccurate in fully determining current temps so i wouldn't harp on it to much.
If this doesn't happen in BF3 and Metro 2033 and really only in Skyrim as you said, then it's probably simply has to do with how that game uses system resources rather then a larger problem with the entire system.
well only reason i think the temp readings are correct. is because i can hear the fan race to 4000 rpms for a couple seconds since is loud as hell... at the same time the temp readins show the cpu socket temp spike to 60 degrees for a couple seconds then goes back down. does this once like every 30 mins or so.
the cpu usage in skyrim never changes, doesn't go more then 60% on any core. the core temp never even passes 50c. So i don't know why its doing it. the game runs perfect. its weird.
but like i said when running prime 95.. after about 20 30 mins. it does the same thing and, just keeps doing it every couple mins.
dell studio xps 7100
amd phenom II x4 820 2.8ghz
hd 5870 1gb
win 7 64