Thanks for the quick reply Zbigniew that sounds quite interesting and is something that I could do with looking at because I'm interested in putting a mathematics section in my Moodle site.
Do you or anybody else have any other information about Webwork.
I would suggest that you first take a look at my integral calculus course from last autumn: https://webwork2.math.ohio-state.edu/moodle1_1_1/course/view.php?id=8&username=guest and click on the course links "Do WeBWorK Assignment X Online"
If you're still interested, you might then visit the University of Rochester WeBWorK site: http://webwork.math.rochester.edu/
You might also look at this early discussion about WeBWorK and Moodle http://moodle.org/mod/forum/discuss.php?d=774 [Note to Martin: I think that discussion should be moved to this forum.]
You might also want to consider this alternative to WeBWorK http://moodle.org/mod/forum/discuss.php?d=1579#6499. You would need to contact Gustav Delius for the Moodle interface code for AIM - I couldn't find it online.
which shows how to plug webwork in as an assignment.
The following link shows how to add webwork questions to moodle quizzes.
The assignment connection is quite stable. The question connection is relatively new and still has some rough edges.