If you need a light-weight Microsoft Project clone, or simply a MS Project viewer, here are a couple solutions :
- OpenProj : http://openproj.org
- GanttProject : http://www.ganttproject.biz
Both can open MS Project .mpp files, so both can do a reasonable job if that's all you want to do. If you want to actually set up a project, OpenProj seems to be the more capable. GanttProject also seems to lack horizontal scroll bars, so I couldn't navigate the timeline well. It also doesn't seem to import predecessors and durations from .mpp files, so again the nod is to OpenProj.