I am going to try to help you out, though I am no expert.
After lots of frustration, I found a post that said that there is a glitch in the 2.2.1 software from T-Mobil that the USB doesn't work right. To get the phone to recognize the USB, turn off the phone, plug in the USB, and then turn on the phone. It will now see the USB.
If you follow this link, Root HTC Magic/Sapphire Android Phone In One-Click
on the bottom of the page is a link to this file: SuperOneClickv1.6.5 ShortFuse.zip
This was awsome because it rooted my phone for me. I had to run it twice to complete, but then it was rooted.
Then download Rom Manager. When done, install clockwork recovery.
I never could get it to boot into recovery mode, but fooling around, I told it to fix the SD card file permissions. This didn't seem to fix the ROM problem, but now the USB works like it supposed to.
I also recomend you download adb wireless. and the whole adb program thingy to your computer.
I hope this helps. I still can't load CM 6.1, but my phone is much faster.