No, the distance cannot be set to a fixed distance. The actual distance depends on a lot of variables -- such as the leading of the regular text on the page above it and the leading and number of lines of the footnote text itself.
But if you find this distance is often too small, check what it says in the Document Footnote Options. Chances are, if you never heard of this dialog before, this distance is still at its default value of 0 mm.
See the Help: http://help.adobe.com/en_US/indesign/cs/using/WSa285fff53dea4f8617383751001ea8cb3f-6f37a.h tml for a full description of the options.
goto: type/document footnote options..
change settings there.
I now see I directed you to the help for CS5.5, and you are still on CS2. Well ... the good news is, there is only one single new feature in CS5.5 since CS2 -- the introduction of footnotes in InDesign -- and so, although this new feature (span columns) seems as badly implemented as the rest of the span/split columns featurette, it won't bother you.
CS5.5, and you are still on CS2.
I should learn to read too!
Thanks for the advise. I think I found a way to set fixed distances
Let's say you want a minimum distance of 4mm above to separator (towards
body text) and 3mm below the separator (towards first footnote). In the
Document Footnote Option --> Layout set the Minimum Space Before First
Footnote to 7mm (=3+4mm) in the Spacing Options box and set the Offset in
the Rule Above Box to 3mm. This appears to work fine!