Hello kachori,
You don't import .pst files in Outlook, you open them. Before installing 7, I simply saved the .pst file to another partition. Then when office was installed, I opened the pst in Outlook and created the mail accounts. All done. All my tasks, email, contacts etc. where all there. If you have a windows.old folder, that pst file should be in there.
Hope this helps,
Gary