first thing is: i only want one pipe | between the items, like in perl join " | ", @$items.

<TMPL_VAR NAME=ID>: <TMPL_VAR NAME=NAME><br>
<TMPL_LOOP NAME=CATEGORIES>
<TMPL_VAR NAME=ID>/<TMPL_VAR NAME=TITLE><TMPL_UNLESS __last__> | </TMP
+L_UNLESS>
</TMPL_LOOP>
[download]

i'd like to be able to control the order of the items from the template (reason: the code is part of a kind of framework or CMS, and i don't want to hardcode it).

From my quick skimming of docs, that doesn't seem possible. Personally, I use the Template Toolkit II for all my templating needs.