1. Download and install Outlook 2010 x64 on the Exchange 2010 Server that has the Mailbox role.
( you can download it from here: http://office.microsoft.com/en-us/outlook/ )

2. You need to create / or to use an existing Universal Security Group. After you have the group, open the Exchange Management Shell and run this command:
New-ManagementRoleAssignment –Name “MailboxImportExport” –SecurityGroup “name_of_group”

3. Add the user you will use to import PST files to the group used at Step 2. After that log off / and log in back on the Exchange Server.

4. Now you are ready to import the PST Files. First open the Exchange Management Shell. After that use the command that fits you best:

a. BULK Import:
Get-Mailbox | Import-Mailbox –PSTFolderPath Y:\PATH_OF_PST FILES

b. SINGLE Import:
Import-Mailbox –Identity “Display_Name” – PSTFolderPath Y:\PATH_OF_PST_FILE.PST
( You have to replace “Display_name” with the e-mail adress/display name/Exchange Alias )

If you encounter any problems feel free to comment / contact me, and I will help you.