If so, how? I have a rather large Word document saved to my computer that I can't edit because my Microsoft Office trial expired.

You just need to open it in Swriter, which is the OpenOffice version of Word. When you install OO you can choose to make it the default for MS Office documents. You can then just double click the file to open it, just like you could in Word.

Yes, you can. Right-click on the Microsoft Word document you want to open, and then choose "open with" Open Office. The rest happens naturally. Remember to "Save As" a Microsoft Word document when you are finished. Open Office can read Microsoft documents, but Microsoft Office can't read Open Office files unless they are saved as Microsoft Word files...hope this helps!

Yes. That's the whole point of OpenOffice.