First, copy the old .pst file to any location you wish. Many choose to place it in the default location with a new name such as "Outlookold.pst". The default location on an XP machine is "C:\Documents and Settings\Yourusername\Local Settings\Application Data\Microsoft\Outlook. It can also be placed in the "My Documents" folder for easy copying at a later date.
Once it's there, follow the instructions in the link below to "Take Ownership" of the file. As before, since you didn't mention the operating system you're using, I'll give the link to XP instructions.:
Once that's done, if the file is set to include all the email and contact information in your normal folders, open Outlook (I'm using Outlook 2007 here so it may be slightly different on your 2010 version), then click on "File" in the upper right, choose "Import or Export", select "Import from another program or file", then choose "Personal Folder (.pst), then follow the prompts to let it overwrite and install to the normal folders you choose..
On the other hand, if you're simply going to add the ".pst" file as a separate "Personal Folder" item in the left hand display, simply click on "File" in the upper right, select "Open", then select "Outlook data file", then navigate to the file and open it.. The folder will show up in the left hand display under "Mail".
Hope this helps.
I recently upgraded to a new computer and installed Outlook 2010. I have Outlook 2007 on old computer. I made an outlook backup of old and want to restore it on this computer but get this message File access denied. You don't have permission required to access this file.
At a loss how to get old files over if this doesn't work.