Lets say i dont trust a third party bitcioin mixer to clean my non-anonymous bitcoins (like btc that i received on facebook or on this forum), but want to be anonymous in my bitcoin exchanges.
I have a couple old PCs laying around, so would it make sense to install the bitcoin client on them then move my funds from my standard PC to one to the other, then back to to the first PC via tor? (Once i am completed with this, i would reformat those other PCs.) The wiki recommends not doing this, but would it work?
No. Each transaction will still lead to the next in the blockchain. Mixers take your BTC and give you BTC with a different history altogether breaking the link to you.
You are right, but the thing is: If I created a new Bitcoin wallet and send some "linked to me" bitcoins, and then spend those bitcoins from that wallet, how is anyone supposed to know Im the owner of the new wallet and not someone else? How is anyone going to prove in court that I am the owner? Its obviously not as secure as a mixer, but I think it still provides some legal protection.