there was something about this back on .com and from memory anything up to 70c is ok and the max temp is 90c, at which point the core starts to set it self on fire lol.
But 64c is abit too high, but its similar to what my 1.4gig amd runs at (50c - 61c without CpuIdle). Thats a thought, go get ya self a copy of CpuIdle, that keep ya system a tad cooler.
Also, i would get all that dust out and brush the fan of the heatsink as well as the heatsink
If you dont want to take the heatsink of your cpu then i would go get some Canned Air (from pcworld or sumthing, should be about £10 a can) and blow that across the heatsink to get the dust out (Warning though: dont hold it in one place for more than a few seconds, it will start to freeze stuff
).
However, you system temp seems to be about right
mines at 35c most of the time...only creeps up to 37 during hot weather again.
hope this helps mate
Dom
p.s - if your going to get a new fan/heatsink have a look on
www.overclockers.co.uk and check out the forum for reviews and what not.