I'm pretty sure your system will have to be reinstalled to repair this damage. Boot from the installer DVD, and do an archive install on you HD; then reinstall all system updates, and any 3rd party software that doesn't work after the reinstall (simple apps shouldn't be affected by an archive install, but anything that hooks into the OS parts of the file system will have to have those parts reinstalled to work right).
If you have a backup, you may be able to recover from that instead.
What's happened is that the Magic Trackpad package has replaced a bunch of parts of your OS -- mostly those having to do with bluetooth, e.g. bluetooth drivers, the bluetooth preference pane, etc etc etc -- with newer versions that won't work right on your OS version and/or your CPU. 10.6 dropped support for PowerPC CPUs, so if you have a PPC Mac the new components are going to be completely nonfunctional for you.