@corf,
Did you figure out the issue? I also have a Antec MX-1 enclosure and only USB works with Windows 7. If I connect the drive via eSATA, Win7 does not see it. If I boot up with the drive attached via eSATA, Win7 boot screen hangs until I unplug the eSATA drive. This worked just fine in WinXP.
If anyone has any suggestions on a possible fix, please post. Everything else on my computer seems to be working just great.
Thanks.