Just a few thoughts to help you make a decision, or confuse you even more.
Remember that the real reason for buying a DSLR is to have access to a lens system. THe DSLR you buy more or less commits you to that system.
Sony is not exactly a new comer when you consider the a100 is based on the assets they purchased from Minolta, so it does have some history. In fact, if I remember correctly you can use some Minolta lenses on the a100. Really only useful if you already have Minolta lenses. The important point here is that Minolta, who had quite a bit of SLR/DSLR history decided to quit the game. If Sony hadn't of come along those Minolta lenses would never have seen a new body. Even if Sony's DSLR venture is successful, DSLR's will never be more then a ripple in the Sony pond.
The story is different with Nikon, and to a lesser extent Canon. DSLR's essentially are Nikons pond. While Canon may be more diverse then Nikon, their corporate image is heavily invested in photography. The point being, there is little chance of either Nikon or Canon leaving the DSLR game.
Sticking with the history lesson just a bit longer, Minolta (and perhaps now Sony) was more likely then either Nikon or Canon to introduce some new cutting edge wiz bang feature. Unfortunately these were not all ways well thought out. Nikon and Canon show more restraint because reliability is more important then flash for most pro's.
Getting back to the lens system itself. I'm not familiar with what Sony has to offer, or for that matter what Minolta lenses will in deed work on the a100. I shot Minolta (7xi) back about 10 years ago, and the lenses were not bad, but there is a reason pro's shoot Nikon and Canon. While you may never buy pro quality glass, buying the D40x at least lets you play on the same ball field should you decide to do so in the future.
So if you managed to stick with my rambling this long, I'll offer some advice. If your serious about a DSLR get the Nikon (or a Canon). Otherwise buy a nice point and shoot.