For those of you using the Dell Latitude D820 and Windows Vista, you should upgrade the Dell BIOS to the new A05 release. It is in the x86 Windows Vista Drivers and Downloads area. One of the fixes that came with this BIOS is a compatibility fix for the SIIG eSATA RAID ExpressCard I use.
To be specific, I am using the SIIG SC-SAE612-S1 card with an external eSATA drive enclosure. In order to use this card with Windows Vista, you'll need the Silicon Image drivers from the SI download area. The x86 RAID driver I'm using for Windows Vista is still in beta but I expect it to be released very soon.
Beware, the SIIG non-RAID ExpressCard fails to work properly with either of my Dell D820's. The specific card I am referring to is the SC-SAE512-S1. When I insert this card, it locks my machine tight as a drum so there is no opportunity to install the Silicon Image released x86 driver at http://www.siliconimage.com/docs/3132-vista-x86-logo-188.8.131.52.zip. If I try to boot my machine with the card inserted, it will not boot and run Windows Vista. It appears to be an IRQ issue, but I do not know for sure. I am swapping the card I have today (if possible) to rule out a bad card.
[UPDATE] I finally got to the office and traded out the non raid card (SC-SAE512-S1) and it worked so the card I had must have been bad or something. The cables are pretty finicky as well, so make sure to test more than one cable.