MySQL

Hi there, we are currently using MySQL version 5.0.22-max-log.
Currently we run into a mysterious problem when running MySQL with
Moodle (moodle.org) which when a lot of concurrent users access our
MySQL database, it "seems" that one of the database tables
(mdl_quiz_attempts) would get temporarily locked and therefore would
generate an error. We were able to reproduce the problem (or to verify
our theory) by manually lock the table for one second and unlock it
right away. More details about the whole issue can be found at:
http://moodle.org/mod/forum/discuss.php?d=69134

Just some quick questions:

1. Is this a known issue (or a bug), that when the MySQL server is
super busy, then it is "possible" that some tables would be locked and
will not be released? If this is the case where could I know more
about this behavior?

2. Is there any DB monitoring software (similiar to Nagios, or
something like that), that could send us a email alert when some DB
tables got temporarily locked up? Or would the MySQL by default log
this kind of incident in the log file? We want to do further
simulation to make sure that the problem IS caused by the table got
temporarily locked up. Any other suggestion how to trouble shoot
this?

Thanks a lot!