Call tracking and/or helpdesk software

I’m going to be managing a small network of approx. 30-35 users, and I’m looking for something to track problems and resolutions. I looked at the website for ‘Liberum Help Desk’ and that sounds like it might fit the bill, but just looking for other input. Until I’ve been doing it a while, I’m not really sure exactly what I will need beyond basic tracking of a problem and it’s resolution, so I’m looking for something either free or VERY low cost. There are no Windows servers in this environment (and I’d like to keep it that way), so that will have to be ruled out as a system requirement.

Anyone using Liberum? Something better? Since this is subjective, points to any intelligent, informative answers.