XSL - Loop through data twice processing differently

[m0nkeymafia]

I have an XSL stylesheet that process an XML document once, and
outputs it how I want it to...fine.
I would like to also populate a "table of contents" based on what XML
is there, which would require looping through the data a second time
[actually this should be done first] and processing it differently.

My question is how can I loop through the data twice [or can it not be
done?]
And if so how do I specify which templates it should use on which loop
round?

Thanks in advance
Chris