Well, there are clearly situations in which the current best offerings in terms of DR (the Canon 5D in 35 mm or better yet MFDB) will not be able to hold detail in both highlights and shadows. The situation you describe could be one of these.
The Sony A100 isn't supposed to be significantly worse/better than its 6MP competitors in this area, and you might simply be running into technological limitations. Those limitations were by the way also present in the film days, and slides would probably be even more difficult to use in these high contrast situations.
Here are however some considerations:
- it is important to distinguish lack of DR and contrasty default curve. I know that my d2x has a pretty contrasty default curve that makes it look like the DR is limited. The shadows are however in fact amazingly clean and it is fairly easy to expand that default behaviour so as to get a much softer rendition. You A100 could be similar,
- Shooting RAW helps getting all the available DR out of a camera body,
- Some RAW converters are better than others at extracting all the available DR. Adobe lightroom makes this rather easy nowadays,
- When the RAW converter cannot do wonders at once, it sometimes help to convert the image twice. Once for the highlghts, once for the shadows, and then to layer these 2 images in PS and manage contrast using masks,
- When that is not enough, you can do what is called exposure stacking. You take several images with different exposures, and the post-process them so as to increase the apparent DR. You can do this manually by overlaying/masking in PS, or use one of the available High Dynamic Range software options available on the market. PS CS2/CS3 has a function supposed to do that, although I am personnally not convinced by most of the results I see. I perfer to used to old manual technique.
For these multi-exposures to work, they need to be taken from exactly the same location, which makes the use of a tripod mandatory for perfect results.
Hope that it helps.