My friend and I did this last year. I lasted until I needed a new bike and bought one. I buy new running shoes and personal necessities, but try to cut back on most other things. I will not buy used underwear, tho. That's my limit. Other than that I frequent eBay, craigslist, second hand and thrift stores for most things I need. I have bought used clothes without a second thought, and have felt much less guilty about all the crap we have as Americans. And I STILL feel like I've got too much stuff around the house (but less and less thanks to donating and eBay).
Good for you for taking an interest in the environment- I wish more people would!!!!

p.s. I don't have any of the things you need, but I like your idea of posting and asking to buy other's used items.