HTC has begun to offer an upgrade that will bring its HTC Sense user interface to the HTC Magic. The update is part of ROM Version 3.03.990.6.
This ROM Upgrade for your HTC Magic will let you experience HTC Sense on your phone. HTC Sense lets you create a phone just right for you. You can customize your experience to be any way you like. Discover intuitive experiences that make everything you do on your phone effortless and delightful.
If you got your HTC Magic from a carrier, using this generic update will cause you to lose any carrier-specific configurations and applications.
I looked at a number of country-specific HTC sites and did not see it anywhere but it appears only to be available from the English Hong Kong site at this time. Hopefully it is coming to other countries and the worldwide site soon.
Note: The update will replace the current ROM image and will erase all user data and programs on your device. Be sure to back everything up before you start.