I can't tell you if you should purchace the K100D, but here are my observations from my experience with the Canon Digital Rebel XT:

Your batteries should last for 200-300 shots unless you use a lot of flash. You should always have two rechargable batteries - one in the camera and a charged one in the camera bag.

The price is unlikely to drop before the middle of January.

I checked the specs on both mentioned Pentax D models. Both will accept four AA lithium batteries. That would be a real selling point to me, especially when contemplating outdoor shooting in subfreezing temperatures. I'm using the AA lithiums in my 35mm *ist with battery grip and can't get them to wear out.

Hi,

The batteries in the DL are AA's or crv's the same as my DS, which is brilliant, I just use rechargable Nimh AA's, and keep a pair of crv2's in my camera bag "just in case". They seem to last me for about 500 photos.

You can also get rechargable lithium ion Crv2's.

As for your other questions, probably, the K100D has the in camera image stabilisation, which sounds good, and the prices will probably come down more, they normally do come down in price, and Pentax are due to announce another dslr shortly for photokina.