The Outlook of version 2007 can read the PST file of previous Outlook versions so there should not be any problem. To open PST file you can use the menu File - Open - Outlook Data File...
You can read how to open the PST file with Outlook and make it Default in
this artickle.
You can also merge the PST content of default User Profile and the new PST by using importing filter of MS Outlook. Note: It will mix the content of both files.