Try this:
In versions of Word prior to Word 2007:
1. Select all the text you want line numbered.
2. Click the File->Page Setup menu item.
3. Click the Layout tab.
4. In the Apply To list box, select Selected Text.
5. Click the Line Numbers... button.
6. Set your line numbers.
7. OK out of everything.
In Word 2007:
1. Select all the text you want line numbered.
2. Click the Page Layout tab on the Ribbon.
3. Click the Line Numbers button.
4. Click Line Numbering Options.
5. Continue as in Step 4, above.
Hope that helps.