Question: I'm using a tablet with Android 2.2. Is there something like `Tab` to switch to the next form field?

Answer: 
Give [androidscreencast](http://code.google.com/p/androidscreencast/) a try. You may already need to have USB Debugging enabled for it to work, but you've said you already have that enabled, so should be ok. It just needs a USB connection to the phone and goes over the ADB protocol.
Use a USB-OTG cable to connect a mouse. You can even make your own by cutting and soldering a microUSB cable to the female end of a USB extension cable.