When clean-installing Windows 7 on my Dell Latitude D810, Windows was able to detect drivers successfully for almost all hardware in my computer. (However I did have to run Windows Update several times to download updated drivers for everything, including the ATI Mobility Radeon X600 graphics card.)
The only hardware that did not work out of the box was the sound card and the Bluetooth. The sound simply did not work, and the Bluetooth light on the laptop was flashing rapidly (despite Device Manager saying the default bluetooth driver was working properly).
For the sound card, I successfully downloaded and installed Dell's Windows XP driver, which worked fine. (Running the R99254.exe file merely unzipped the drivers, which I had to install manually in Device Manager)
The Bluetooth card required more effort. Dell's XP driver does not work, and for this system Dell does not offer any Vista drivers. However, I was able to figure out that the bluetooth module in this computer is a Dell Wireless 350 Bluetooth Internal Module, and with a bit of Googling I found a Windows Vista 32-bit driver for this card for the Latitude D820 machine. However the module is the same, and after installing it I have full Bluetooth support.
I downloaded this bluetooth driver from:
Drivers and Downloads
The installer updated my Bluetooth module firmware and installed the driver.
I am now running Windows 7 with no problems on my Latitude D810 - in fact it is running better than Vista!
Good luck!