Some time ago I talked about installing a custom ROM on your HTC Magic, to enjoy the greatness that is Sense UI. I mentioned that HTC was working on official updates for the Magic and now it appears to be available everywhere.
I'm not sure where you can find it, but for Danish users it is available here.
All you have to do is follow the instructions and it will automatically update on top of whatever ROM you are using.
Remember that updating will delete all data and settings on your mobile, so BACK UP FIRST!
If the update cannot connect to your phone you might have to install the latest drivers by installing the latest version of HTC Sync (it should be available on www.htc.com somewhere). For Danish users it can be downloaded here.
Good luck with your update and enjoy your new awesome phone :)