You can't really move the posts themselves, but you can move their contents.
So let's say that we have the following:
Post 1: Blah Blah #1
Post 2: Words #1
Post 3: Pictures #1
Post 4: Blah Blah #2
Post 5: Words #2
And I want to move "Blah Blah #2" to where "Words #1" is and everything else down, I'd do the follow:
Modify the post that contains "Words #1" and selected the relevant piece, cut it from there and paste it below "Words #2". Maybe throw in a horizontal break so I can make sure to notice the difference. That leaves that second post completely blank - I can then take "Blah Blah #2", copy the contents of that post, and move it. #2 is now right and post #4 is now blank.
Then just repeat the process until its in the order you want. And add additional posts if you need.
That make sense?