I bought one of the manual "hound dog" aerators and Home Depot. How far apart should the holes be spaced?
as close as possible. you need to go over teh entire area several times.
Like a machine aerator 6 inch on center.
"Like a machine aerator 6 inch on center."
From what I've seen not all machines are the same and with some it's recommended to make multiple passes to get the holes per square foot you're looking for.
I have the same aerator and found this page with info on hole spacing using a turf hound aerator useful. It's towards the bottom of the page.
For the reference of others, There is a tool rental at HomeDepot now, so you can rent a mechanical aerator from them rather then spending good $ over buying a manual one.