myspace account is your own account created on myspace ( you can't sell it ) while myspace bulletin is your own message board/forum that you and all your friends can see and reply to. (some sell it, some do an exdeal) esp. if you have myspace contacts as high as 10,000 and above.
The thing about bulletins is that if you have hundreds or even thousands of friends, you will see hundreds of bulletins posted in a day. They are not like an email where you have a copy of the message forever; bulletins expire in 10 days, and I think you can only see the 250 most recent ones. It's a good way to get your message out, but no guarantee everyone of your friends will see it.