As noted in a prior post, I have had issues getting eSATA drives recognized off the motherboard eSATA connections, as have a lot of other people.  In my case, the motherboard is the well respected Asus P6TD Deluxe but I could not get a Western Digital MyBook to be seen at all.

I had the same issue on the Mac Pro with the new Drobo S so I bought two different eSATA PCI-e cards, one for each machine.  The one in the Mac is the Sonnet Tempo E2 and the one in the Windows box is a LaCie SATA II 2E.

Both systems work great, but to focus on the Windows issue; the BIOS on the Asus Board immediately recognized the card as a SATALink and enabled it.  Windows 7 needed to start up completely without the drive connected to install its own device drivers.  I’m glad it did as the drivers in the box from LaCie were pretty old, and once again the Microsoft drivers did the job.  As soon as Windows told me my device had been installed, I powered up the WD drive and Windows 7 found it and mounted it properly.  Now instead of FireWire 400 I have an eSATA connection at 3GB/s.  So if you are thinking about an eSATA drive for your Windows 7 machine, factor in the requirement for an eSATA card, about $50 and things should be good to go.