I've been using Open Office for a while, so that I can open and work on school produced documents from Excel and Powerpoint at home, and vice versa, without the personal outlay for work programs when I can use MsWorks with Word for my own stuff.
I've just gone paid for with Star Office, which has a manual, and am transferring over my Works files - a few problems with the spreadsheets which are taking time, but the format they are saved in is much smaller, it's going to give me much more space. The graphs in Calc are not so flexible as in Works, though, so I may have to keep it installed. Not up to Excel, definitely.
But all the programs will save in MS compatible formats (even if they don't come out the other end exactly the same - they need tweaking before running a presentation!)
Our hardware supplier has started offering Star Office as an alternative to Office, so I need to assess it for school.