Some of you might already know how to build Android source code for Android DevPhone rev.1 / T-Mobile G1 (aka HTC Dream) / HTC Magic (aka HTC Sapphire). If you don't know how to build, try the instructions in this page.
However, since HTC Magic has 2 versions (PVT32A / PVT32B), the rom images built from the Android source code might only work on PVT32B version because the bootloader / radio images are different. You better watch out for the differences.
After you build the rom images for your device, you can use the fastboot tool in the folder to flash your device if you have already flashed engineering bootloader into your device.