I followed another set of directions not using DD-WRT but using Gargoyle which is another firmware. You can do it either way, but it depends on if you can actually follow the instructions LOL! Take a look through http://www.dslreports.com/forum/r22483979-Repeater-with-WRT160N
as it talks about the same thing if you are still looking to do it. If not you can always stick with getting a new repeater as most of them double as a router and repeater... well some models do anyways. I'd recommend http://www.wifirepeaterreviews.com/exm/Linksys_Repeater/
for some of the newer linksys ones.