Install / uninstall script

Hello,

     I am developing an extension which should support Firefox 2 and Firefox
3.

I want to run a script as part of installation/uninstallation process so
that I can copy/clean/update the shared files in someother dir.  Is it
possible to add it as part of xpi file?

I looked at install.rdf options, but I could not find any option to do that.

Where can I find more information?

Thanks,
Anna