Post as another user / change post date

[storpappa]

I am starting a new site and need to upload some prior activity. Rather then just label the thread titles 2008-01 aaa 2008-02 aaa
I want to post the threads with the correct date so future searches look accurate.

Is there any easy way to make posts or a mod that will let an administrator make a post and choose
A - the user name for the post
and
B - the date / time of the post?

Thanks