i made a test using LibO4.2.4.2 running on XP/SP3
Text direction:
I selected a cell, or a row, or a column, or all cells of a table and changed the text direction using the tool:
Indent
I selected a cell, or a row, or a column, or all cells of a table and changed the text direction then:
Format > Paragraph > Indents & Spacing and selected the indent I wanted to have.
The same should be possible in Writer.
If my answer does not solve your problem, please advice on all steps you took and their results. Also advice on LibO version and OS.
EDIT:
@aapthorp - I am sorry that the Indent-topic is not yet solved. I made again a test but did not select the cell but only the text. In this case it is not possible to change the direction of the text. Other attempts to change the directions with selected text where not successful as well.
I assume now that there is a difference between LibO on XP and Ubuntu. However, you might also need to suspect a bug.
Here is some more information on a different case in AskLibO; maybe it helps: LO Writer: table text orientation