Your contacts should have migrated automatically along with the rest of your Outlook data, but here's a quick workaround anyway. It involves exporting the contacts from your old computer running XP and importing them on the new PC running Vista.
On the XP PC
, open Outlook and go to File -> Import and Export. Choose "Export to a file" from the list, and hit Next. Choose "Comma separated values (Windows)" from the new list and hit Next. When asked what folder you want to export, select the one marked Contacts. Save the file onto a USB flash drive, CD, or somewhere else that the Vista PC will be able to use it.
On the Vista PC
, open Outlook and go to File -> Import and Export. Choose "Import from another program or file" and hit Next, then choose "Comma separated values (Windows)" and hit Next again. Browse to the file you saved, then click Next to begin the export.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 6.1 x64; en-US; rv:1.9.2a1pre) Gecko/20090710 Minefield/3.6a1pre
Laptop: HP Compaq nx6325 - Turion 64 X2 @ 2GHz, 2GB DDR2, 100GB HD, ATI Radeon X300, 15" LCD, Seven Pro
Handheld: Palm Treo 650 - Intel PXA270 @ 312MHz, 10MB RAM, 32MB flash, 2.7" LCD, Palm OS 5.4