As far as I am aware,all Outlook info is stored in the Outlook.pst file. Back this up to a floppy or disc or 2nd HDD then import it once you have upgaded your OS. See click here for this Outlook add-in. I used this when going to XP from Me and I'm pretty certain it included contacts - somebody else may confim this (hopefully ;-) )
For Contacts only see the help file in Outlook for saving contacts in a folder.