Good god people here are a suspicious lot.
This has been my biggest problem trying to get into the bitcoin economy. I'm hoping to win a few things on biddingpond.com so I'll have some history.
Is the Windows 7 still available? Feel free to PM if it is.
I think the best way to do it is buy something exactly like you would in an other medium and then provide good contact information.
Of course if you want to remain anonymous then you can't do that. That goes for sellers too.