1. Find both of the PST files. I am assuming that you have both OSs on the same drive and fat32. If the W2K install is in NTFS then you will need to put the PST file on a FAT32 drive(hopefully the one that you intend to use is the 9X one if not then I will cover that next.)
2. Once you have the locations of all of the PST files determine which one you want to keep and either write down the path or copy it to a folder called Outlook(also do this if the pst file that you want to keep is on an NTFS partition or drive) Then delete all other copies of the PST file.
3.Open Outlook and you will be told that it(Outlook) cannot find the PST file and it will give you an open file window to prompt you to locate the PST. Navigate to the Folder and open the PST.
4. You will have to Do this in both OSs with Outlook.
I do this on a slight variation with a mapped network drive and use the same PST on 3 machines. The only thing to be careful of is opening it in multiple instances at the same time.
PM if you have any questions.