|VueMinder Calendar is compatible with XP and Vista too. I think it mentions that on the website, but isn't very clear.|
Transferring data between computers can be done by backing up your data on one computer and then restoring that data on the other, using the backup/restore capability built into VueMinder. I've transferred data between computers several times, and it's all very seamless.
If your computers are going to be networked together, you can also share your calendars to your local network and transition the data that way (using Pro version only), but I think the backup/restore approach is probably easier, especially if you're not planning on continuing to use your old computer and don't need to share the data with other computers on your network.