If you know where it is at then Open Outlook and go to File ->Open->Outlook
Data File and browse to the location of the file, select it and click OK.
If you do not know the location then search your harddrive for *.pst to
locate it. First you will need to make sure that you are showing hidden
files and folders and file extenstions for known file types. If you need to
know how to change those let me know and I can send you steps.
I hope this information is helpful.
Robert Findlay
Partner Technical Lead -- BizApps
Microsoft Technical Support for Platforms and Business Applications