...then you may have the wrong collating order set in your postgres installation. Try this query:
select deci, ascii(code) from tree_encodings order by code limit 5;
The results should look like this:
deci | ascii ------+------- 0 | 48 1 | 49 2 | 50 3 | 51 4 | 52
If they don't, you need to do an initdb with LANG=C. See this thread on the PG mailing list. Having the collation order wrong causes the tree support to fail; acs-content-repository not installing is a side effect of this.
The bigger question is do we want to require a specific collation order to run OpenACS? Especially as it's a pain to change if you've got it wrong.