You are absolutely right that WIDCOMM refers to the Bluetooth modules and Sigmatel refers to the integrated audio chips (not only sold by Dell, but also by HP, and probably other companies)
As far as WIDCOMM, I have not heard of any modding being done, however there are some threads concerning the newest versions of the WIDCOMM drivers. WIDCOMM seems to release drivers very secretly, and so it's a pain to try and figure out what the newest drivers are so you can download them, but some threads have been tracking them. Back when I bought some Bluetooth headphones and they didn't work, I did some research and found out that Dell was providing a very old Bluetooth driver, and it turned out that the newest driver (downloaded off some weird free-drivers website) had headphone capabilities, so it essentially fixed my problems. But again, I have not heard anything about WIDCOMM modding. I started a thread, I think it was titled something like "Bluetooth problems SOLVED!" but I have not updated the download links and they have expired, so in that case no the download links will not work. But I'm sure there are other threads that would have current download links. I am now completely happy with Vista's Bluetooth support, and everything works so I don't keep track of WIDCOMM drivers any more.
The Sigmatel thread is basically about unlocking some hidden features in the driver. The Sigmatel control panel applet has been reduced to one useless checkbox, but we found some hidden tabs and plenty of extra options. These include an equalizer (if you don't know what that is, look it up) and stereo mix / what-you-hear recording device, for recording anything that you can hear (sort of like a microphone that picks up perfect, digital quality recordings of anything playing in the computer - useful for playing music over a Skype call/podcast or recording internet radio) among the most useful. There is also an option for allowing playback out of your microphone port, which would basically mean 2 people could have headphones plugged into the laptop and listen to the audio - one of them would use the microphone port, the other would of course use the headphone port. I don't remember the other options off the top of my head but those are the biggest. Apparently these features are working in Windows XP, however I am using Vista Ultimate and the configuration files have not been modded for Vista yet...
So there's the basic rundown. If you have any more questions, ask away!