using the PEAR-class for information?

hi all! i'm trying to fetch some information about pear, for example which packages are installed (or the other way round, i wanna know if a given package is installed). i tried looking at PEAR::Info, but that didn't answer me how to query PEAR for installed packages... so is there an easy method to check if a package is installed by querying a class? i don't want to do a @include to test it, i want a native answer from pear itself ;-) hope you get what i mean... bye, stephan