The file you posted on here was a .zip
The file you said it was was a .doc
Which is it? a .doc zipped in a .zip?
The .doc corresponds with Microsoft Word, so you'll need Microsoft Word to open it.
.zip means it's just a zipped file, any mac with 10.4 can open it using the OS, otherwise you'll need software to open it.
If you don't have Microsoft Word, tell your source to save it as a RTF (Rich Text Format), and not to send it over in a .zip. Any computer (at least any mac) can open a RTF using notepad.