I agree with the afore mentioned posts. You should always get the money first, then send the item once you are happy with the transaction.
As a buyer, you send the money first, but should always keep your receipts for proof of sending the money and having made the funds (in check/money order/etc.) available to the seller. You need to keep these for your own personal record for about 3-years so no one can ever come back and claim you didn't pay for an item or made only a "partial payment". It's just good book-keeping and always helps if there's ever a question.
Hope this helps you out, Nick.
- RCT