Symantec's upgrades are generally based upon how long you've owned a product. They inform you based on the version of your product if the upgrade is free, discounted, or for an appropriate amount. I really don't believe they have made all that many upgrades for Ghost though they have several flavors of it. If there is an upgrade, each is handled differently. Sometimes they only let you go through their liveupdate; other times they provide a file to download and run. If it is the latter and you know your version, you can download it to any computer, burn it to a CD and install it on you W2K machine.
This is just me, but if you have used Ghost and it works, leave it alone.