Well apprently if it used a Prescott, Cedar Mill, SmithField or Preslar Pentium D then it should, however, if you were using say DDR memory on the board, the Core 2 only use DDR2 far as I know, so this might prove an issue. Full support for the cpu would best be checked on the manufacturers website.
A Core 2 Quad would be the best option vs the dual, cause if it can work with a lower end say a core 2 Pentium, then it can work with the high end Core 2 or core 2 quad at least the vast majority of the time. Best dual core, Core 2 E7200 to E7600 or E8300 to E8600 and up, for the quads Q6400 to Q6700 or Q8200 to Q8400 or Q9300 to Q9650, the 8300 and up are the best choice or the Q9000 and up the best choice in regards to performance.
Conroe was the offical replacement for Pentium 4 and Pentium D, so if they use the same socket I am 99% sure they would work, as long as the memory used as well as the wattage/FSB lines up.
So, is it worth it, might be if you can get them cheap enough, but last time I checked about 6 months ago, to go from E8400 to Q9550 was like $320 whereas a brand new cpu that was faster then both by a good amount was $110 not including motherboard or memory. So this is up to you
