As far as I am aware Outlook 2007 doesn't automatically launch when you use "send to e-mail". It seems to remain in outbox until Outlook is opened. This is certainly what happens on my Vista machine.
It can happen that Outlook doesn't close properly and a "hidden" prog remains running and is listed under processes. I have found that this used to happen when I had a mobile phone, operating Windows Mobile, still connected which had synced with Outlook.
I think you need to check what is keeping Outlook open in the background and possible run MS Office diagnostics and see if it finds any problems.