Let's face it, MS Project costs real money. If you're a small company, buying licenses for it will eat up your project margin faster than you can say - well, "margin". However, don't despair - there are free Project Management tools around!
One: OpenProj. Best free PM application ever.
OpenProj by Projity is a desktop replacement of Microsoft Project. OpenProj has equivalent functionality, a familiar user interface an even opens existing MSProject files. It does Gantt Charts, PERT charts etc. Available on Linux, Unix, Mac or Windows, and it's free - how much better does it get? Review here, Download here.
Second: Zoho Project.
The team at Zoho is one of the coolest "Web 2.0" companies out there. Their online office suite includes tools for word processing, spreadsheets, presentations, databases, note-taking, wikis, CRM, project management, invoicing and other applications. Being web-native, all Zoho applications are operating system independent. It supports creating tasks, ownership, setting deadlines and tracking milestones; working with calendars, Gantt charts, reports, share supporting files—all the cool features expected in a project management package.
The major difference is that while one can debate the merits of online/offline for individual productivity applications, project management by definition is team-work and as such a natural fit for the Web. Zoho Projects is free for one project, and has a scaled price structure above. 12$ a month gives you 10 projects and 2gigs of file storage. And, even better - if you're running an open-source project - well, it's free. "Beer" free.
Third and last: Ganttproject
Another free alternative - a little less fully featured than the others, but from my experience, the developers take the time to listen to their users (heck, they've incorporated some of my suggestions!). On their website, they claim that "This set is enough for most people (remember that 80% of MSProject customers use 20% of it's numerous features)" - which is probably true, I know I might use 35%, and I'm a heavy user :). Your mileage may vary, of course.
Best news: platform independent(ish), works in Java (so you need a Java Runtime Enviroment if you're running Windows), and free for any kind of use.
More at: http://en.wikipedia.org/wiki/List_of_project_management_software - but I've tried all of these, and wouldn't hesitate to recommend them!