In order to use KAlarm, you need to run KDE 2.0 or later. KAlarm uses the libraries libkcal (slightly updated), libical, libicalss and libicalvcal from the KDE package kdepim version 2.2.1. The standalone KAlarm package comes in different versions which contain the appropriate sets of libraries depending on which version, if any, of kdepim you have installed.
KAlarm uses about 8 Mb and the alarm daemon uses about 5 Mb of memory to run, but this may vary depending on your platform and configuration.
You can find a list of changes in the ChangeLog file, or at http://www.astrojar.org.uk/linux/kalarm.html.