How much memory is in your system? 64 bit before SP1 would not install with more than two gigs in the system. So if it installed with SP1 my guess is you have more than 2 gigs of memory. 
I have an XPS 700 with Win XP.  I popped in the Vista x64 disc and it will load the windows files into memory then blue screens.  According the error code it looks like it cannot find the SATA drives.   i have the 1.4.1 bios and everythign else looks like it up to date.  What gives?    (i have a Vista capable sticker on my machine...)  
XPS 700 - upgrade vista 64 / blue screen