See also Orca bug #465468 which is blocked by this issue.
http://bugzilla.gnome.org/show_bug.cgi?id=465468

(There doesn't seem to be an entry for OOo-dev 2.3.0 in the "Found in
version:" list on the bug report web page).

This is with OOo-dev 2.3.0 (build #223) Linux RPMs on Ubuntu Gutsy
(with all the latest updates and with Orca from SVN HEAD).

I've been working through the simpress tutorial at:

http://www.ischool.utexas.edu/technology/tutorials/office/impress/

I got as far as the instructions on:

http://www.ischool.utexas.edu/technology/tutorials/office/impress/01c_alt_view.html

The slide presentation area has tabs for

Normal, Outline, Notes, Handout and Slide Sorter.

By default, the Normal view is shown.

I changed views to the Slide Sorter View with the View->Slide Sorter 
menu item.

Here's what the tutorial says:

Slide Sorter View -This view allows you to preview your presentation 
slides as thumbnails. You can insert, delete, copy and move your slides 
around in this view.

To manipulate your slides in "Slide Sorter" view :

    * Go to View->Slide Sorter.
    * To rearrange slides, click on the slide you wish to move, hold down 
      the mouse button, and move the object to a new location in the 
      presentation (between slides, at the beginning or at the end). Lift 
      up on the mouse button when you are satisfied with the new location. 
      A vertical line between the slides indicates the position to which 
      you are moving the slide.
    * To return to Normal view, go to View-> Normal.

Now usually, when an operation requires mouse drag&drop, then in order
to be accessible, there should be equivalent functionality available
for use with the keyboard.

I do not see any such functionality for this operation.