Besides checking/reapplying the heatsink compound, check to make sure the HSF is seated all the way. Don't know about that Vantec cooler, but I've seen problems with coolers which clips on to all three lugs on each side of the CPU socket. Some heatsinks are large enough that there is a notch in each end for the clip to come out of, and if the clip then extends to each side to engage the side lugs if the heatsink isn't properly centered the sides of the clip may sit underneath the heatsink.
Another thing to check... if your CPU temperature is being reported properly. Motherboards don't necessarily report the temperature properly. A friend of mine has a P4 in a Soltek board, and the CPU temperature stays at 0, LOL. I have a VIA C3 system where the CPU temperature is reported as much lower than the motherboard/ambient temperature. To more accurately check the temperature you'll need something like those LCD displays with a thermister on a wire.
Since not overclocked, VeggieMan's suggestion of lowering voltage is a good one.
If all else fails, pick up an Athlon XP 1600+ for cheap and some cheap HSF like the ThermalTake Volcano 7 - probably $70-80 out the door. This CPU doesn't run as hot as the Tbirds and the Volcano 7 is more than adequate to cool it at default speeds. As a bonus you get a nice speed boost.