There's supposed to be instructions on the 'net for building your own bike trailer, that's one way to do it too. That Chainbreaker Zine sounds great!
I'm like as not going to do my post office trips walking with ye olde Radio Flyer wagon, it's not that far and that's the easiest solution for now. I eventually want to get another bike that's more touring oriented and put a rack and panniers on it. I may look at a bike trailer but I'd want to be one I can easily unhook from the bike and tow in with me into the p.o. - that's really the only use I'd have for a trailer right now.
If taking the laundry to the laundromat is all that's keeping you from going all-bike, then think about it: $500 a month or $700 a month or whatever it costs you to run a car, just so you can drive it to the laundromat???