When you talk about moving the database from BES 3.6 on MSDE 7 to BES 4.0on MSDE 2000A, this can't be done like that.
The options for moving a BES and upgrading are 1 of 2:
1. Upgrade the BES to 4.0 on the current hardware then move to new hardware
2. Move current BES 3.6 to new hardwar then upgrade to BES 4.0
Option 1 won't work for you because of Windows NT, so you will need to move your BES 3.6 to the new hardware and then upgrade to BES 4.0. You can't change BES versions when moving between machines, it just doesn't work. In the process you will want to have MSDE 2000A installed on the new hardware first. It won't matter if your database was on MSDE 7 either.
Upgrading MSDE to 2000a won't do anything to your database, it's the BES 4.0 upgrade that will update your database. But if you are on MSDE 7 when you try to upgrade the BES will tell you that the database engine is too old.
To install MSDE 2000A easily follow these steps:
1. Download MSDE2000a.exe from Microsoft
2. Run the MSDE2000a.exe, this will extract the files to a folder called MSDERelA on the root of the C drive
3. Open a command prompt and navigate to that directory
4. Run this command, Setup SAPWD=(Some password)
You can use any password you want but I've never seen it used for anything after that, at least in the BES world anyways.
The aboce command will install MSDE for you with the default name of MSSQLSERVER, the default name is always easier to work with incase you have to run any queries.
One thing to keep in mind if/when you move to Exchange 2003 you will have to do some extra things for your BES function as it should:
1. Remove the Exchange 5.5 Adminstrator from the BES and install the Exchange 2003 System Management Tools only
2. Set permissions for your BESAdmin on Exchange 2003 as it is different then 5.5
This article will help with the process:
BlackBerry Search Results
Hope this clarifies things for you a little more.