Yeah, we had the same problem, but it was more of an issue of not knowing who had worked on what and what the status of each issue was. So we wrote our own using php and mysql. Then we setup a user called "helpdesk" which is aliased in/etc/aliases to a perl script that parses the message and shoves it into the database. You can also add new tickects from the web page. If you want the code we'd be happy to send it to you. There are also likely to be a good number of open source utilities already out there that more or less do the same thing. do a little searching on sourceforge and freshmeat.
good luck,
0taku