Are you using the dirvers from Intel or Dell during the installation. Should be using the drivers from the Dell support site: http://support.dell.com/support/downloads/download.aspx?c=us&l=en&s=gen&releaseid=R173412&SystemID=DIMENSION%205150/E510&servicetag=&os=WLH&osl=en&deviceid=16825&devlib=0&typecnt=0&vercnt=1&catid=-1&impid=-1&formatcnt=1&libid=41&fileid=235720

The Dell version of the Storage Manager is available here: http://support.dell.com/support/downloads/download.aspx?c=us&l=en&s=gen&releaseid=R173416&SystemID=DIMENSION%205150/E510&servicetag=&os=WLH&osl=en&deviceid=8615&devlib=0&typecnt=0&vercnt=2&catid=-1&impid=-1&formatcnt=1&libid=41&fileid=235727

What are the raid errors you are getting?

When Vista does it's reboot during the install process, the Intel Matrix ROM says that there are disk errors and Vista can't start.  FYI, I was using the Dell install process drivers using the Vista "add drivers" method during install. The install process is also extremely slow. 

I managed to do a workaround, as follows:

1. Installed a 3rd hard drive (PATA in this case)
2. Installed Vista on the 3rd drive with the raid on the 2 SATA drives enabled (installation only took minutes).
3. Booted to Vista and installed Dell version of Intel's storage manager (v. 7.x).  My understanding is version 7+ turns of LPM which is what causes the Vista issue.
4. Used Norton Ghost 2003 to do a disk to disk clone from PATA drive to RAID drive.
5. Rebooted w/ Vista install disk and chose "repair pc" which detected an error with the MBR (Norton 2003 is not compatible with Vista's MBR).  Vista fixed the issue.
6. Rebooted and everything works!

Not the worst thing in the world but definitely something that Dell/Microsoft should have addressed appropriately. All they need to do is have a way to disable LPM during install.  Seems like this wasted a lot of people's time.