At the moment I'm using B7T9, but I've also used B7U9 without issue. The problem you described is a known one and causes the exact issues that you detailed in your first post. Just replacing the NVidia drivers with the Microsoft ones would have been sufficient to completely correct that problem. Upgrading to one of the later 1620 firmwares would allow it to work perfectly with either set of drivers.
In your first post, you described a number of things that you previously tried in order to correct this issue. I'm assuming your system was stable prior to adding the 1620 drive. Could you have caused a different problem that somewhat resembles your original problem by your earlier troubleshooting attempts? Are the symptoms 100% identical to your original problem?
Did you add anything else to your system lately - at about the same time as you added the 1620?
Is your drive running in DMA mode? Are you sharing the IDE cable with another drive - if so, consider temporarily removing it to see if the problem goes away. Set the 1620 as IDE master if it's not already to see if this has any effect.
Consider running a memory test program overnight to make sure your system is working correctly. Microsoft has an excellent one that I like at http://oca.microsoft.com/en/windiag.asp. It found problems for me that MemTest86 did not.