There has been a certain amount of discussion (in great part by me) on controlling the naming of IMAP PST files in Outlook 2010.

I just found how to do it:

Brief note in front: I set up a dummy account initially to get Outlook used to where I wanted the data files -- I use the "old location" of C:\Documents and Settings\%UserName%\Local Settings\Application Data\Microsoft\Outlook\data.pst as opposed to putting them in my Documents folder like Outlook does now"...

When I set up the account, I selected to configure the account manually.
Then I filled in the user info, server info, and login info on the first screen;

Then I went to "More Settings" and filled in the Mail Account Name.

After that, I returned to the first screen and finished off the date, and then walked through the other tabs and filled in the necessary fields -- like server port numbers.

Then I just finished off the account info and closed it as "normal."

Outlook then created the data file (PST file) and named it to match the Mail Account Name.

As it is an IMAP account, I didn't have to worry about importing of prior data etc.

Why Microsoft didn't just tell us that, I haven't a clue.

Worked for me, hope it helps others.

Chuck Billow