You need to understand why open source is important to your requirements -- is it price, access to source code, unique features and functions, ability to customize? Open source programs are technically free, yet there's no such thing as a free lunch (have you heard that before?). You need to consider training, documentation, enhancements, bug fixes, and the entire infrastructure required to develop/test/run the system -- all the usual stuff that goes along with most software projects. Regarding "how they work" I recommend you read the brief article about open source software.
For more information, browse our Learning Guide for Open Source CRM.
This was first published in June 2005