I will try to fix errors as soon as possible. Sometimes feature-requests can be fulfilled promptly, too (this depends on the requested feature, of course).
Smaller updates are free. Check for updates at the website or, even better, register for the mailing-list.
In case I will make changes to Archimedes that increase the value of the software significantly, I might ask for an upgrade-fee. This is not planned for the near future (not before 2009, definitely!).