Dell XPS400 Vista RC1 and RC2 problems

I've been trying to run RC1 and RC2 on my XPS400 for the past several weeks.
Beta 2 seems to run OK.

RC1 installs fine and I can even use it for a while - until I reboot the
first time. After the reboot, I get to the black screen with the loading
progress bar scrolling. It seems to go an initialize the USB controllers
(the keyboard and mouse lights go off) and then nothing else ever happens.
The machine sits at the black scolling screen forever. Nothing helps.

RC2 won't even install. I get past the "Windows is loading files" part,
then the black screen with the scroll bar flashes for an instant and then I
get a BSOD. "Driver_IRQ_Not_Less_Or_Equal" and then further down
"ataport.sys address 82f6295f base at 82f5c000 datestamp 45234bcf" what ever
that means. I know it means one thing - no RC2 trials for me!

So, can anyone help me? I've tried a BIOS upgrade, no luck. The machine
runs XP Pro just fine (as well as Linux for that matter). I'm currently
running a freshly installed copy of Vista Beta2, which is bit sluggish
compared to XP Pro, but it is running.

I've done a bit of googling, but only thing I can find deals with NT and Win
9x/2k. Not much in the way of Vista support info on the net yet.