I would try what kegobeer suggested.
All of your vista 32bit drivers will work in Win7.
Once you get it installed, let it run for a while, Win7 will install drivers but you may need to change a couple. I think I changed two.
I wouldn't hold my breath waiting for Dell to come up with the Win7 drivers for your computer.
Dell doesn't support Win7 for mine either, I've been running the RC x64 since May and now Ult x64, both clean installs. No driver problems.
If the Dell ACHI/RAID controller doesn't work, get your ACHI RAID controller from Intel.
If you want to do an Upgrade install, get the latest Vista drivers from Dell and install all of them. Install the BIOS update.
Then try the upgrade again.
Put the AHCI/RAID controller on a USB stick and add them during the install, you will need to do a Custom/Clean install to do this. Boot the DVD and choose Custom.
Let us know if you have any questions.