If you have a Pocket PC running the Pocket PC 2003 operating system, you may be able to upgrade your device to the Windows Mobile 5 OS if an upgrade was released for your handheld. 

You can purchase these upgrades from your Pocket PC's manufacturer or you can try eBay.com, which offers select Windows Mobile upgrades at substantially lower prices. Below are listings of Windows Mobile 5.0 upgrades available for auction.  Check the auction listings for device compatibility.