Yesterday I struggled with how to update a Vodafon HTC Magic to Android 2.1 (which I urgently needed for testing purpose). The offical update has not yet been published, although several blog posts from spring 2010 stated, that this summer an update will arrive. In case you’re in the same situation, here’s my resumé.
!!! DISCLAIMER: NO WARRANTY! YOU COULD RUIN YOUR DEVICE !!!
First I recommend cyanogenmod. Go to their wiki and follow the instructions: http://wiki.cyanogenmod.com/index.php?title=HTC_Magic. Thanks to their nice write up, I discovered the first important thing: I have a HTC Magic 32B. So, the next step is to proceed to the Full Update Guide – HTC Magic 32B. Read it carefully! And also, if you live in Europe, read the last section! For me, I saw the three skateboarding Androids in the fast boot menu (access it with back + power on). I got the “Incorrect Model ID” error after loading the SAPPIMG.nbh, but didn’t need the goldcard part! I just followed the “Non-TMobile 32B Magics and ION/ADP2” section – everything worked fine. Maybe it’s just me, but after that step I restarted the “old” system, and also copied the backup on my PC…just to be sure.
Now proceed to Upgrading From CM 4.2 or other rooted ROMS to 5.0.x(Dream/Sapphire). Don’t get overwhelmed, it’s a straight forward process. The important thing is, to perform a FULL WIPE. First I only cleared the dalvik-cache, which resulted in a never ending boot phase. Then I tried again with a full wipe, and it worked like a charm!
And that was it. Hope this helps…the whole process took me a few hours, but if you do it like described here, you can do it within half an hour (including all the downloading 
).