How do I control text alignment in a document with a  3 column layout in Pages 09?
If you've got tabular data (which it sounds like you do), using a table is perfectly appropriate.

The other way is with tabs. Show the ruler by hitting command-R (if it's not already visible). You should see triangles denoting the margins of the page. Click anywhere in the ruler to create a tab stop. Create some more. By default, tab stops are left-aligning, but if you double-click on an existing tab stop you cycle through center-aligning, right-aligning, and decimal-aligning (useful for lining up numbers like $100.10 and $100.).

Once you've got your tabs, start entering some text, with tabs where appropriate. If you want to adjust the tab stops, make sure to select the text it applies to first.

If you want to get really smart, once you've got everything set up exactly the way you like, you'll create a style. Hit command-shift-T to show the styles drawer (if it's not already visible), and click the + at the bottom of the drawer. Create a new paragraph style and call it whatever you want. Then you can apply it consistently to new text in the document.

Using columns to do this is possible but awkward. Using spaces is a bad idea because the text will never line up right—plus it's a PITA.