What with Jam Packs which don't appear software-instrument browser?

Did you have the Jam Packs installed in GarageBand '09? And how did you upgrade? Did you uninstall GB '09 before upgrading and erase GarageBand's library files?

If you did not uninstall anything, your Jam Packs should be still installed. Then it will probably help to rebuild the loop index.

See this support article on how to rebuild the loop index: Rebuilding the Loop Index in GarageBand

But if you uninstalled GarageBand '09 before upgrading, you will have to reinstall your Jam Packs. What is your MacOS X version? With Snow Leopard or earlier simply insert the Jam Pack DVDs again and run the installer.

If you are using Lion or Mt. LIon, some of the old JamPack installer DVDs will no longer work. Then post back, please.

Regards

Léonie