associating xml with xsl

Hi,

I'm doing a site for which xml content needs to be delivered three ways

1)
(raw xml, xsl stylesheet is a dont care)
http://site.com/somefile.xml

2)
(transformed xml -> html via xsl stylesheet)
http://site.com/somefile.xml

3)
(transformed xml -> html via xsl stylesheet, php accepting additional params)
http://site.com/transform.php?file=somefile.xml

(#2 and #3 use same stylesheet)

Given this goal, I'd like some advice on how to associate style sheets
with xml documents, I'm stumped on the intelligent way to do this :(

Note that not all xml files will use the same stylesheets.

It doesn't appear I can use <?xml stylesheet ...> because in #1 the raw
untransformed xml needs to be accessed and the stylesheet PI seems to
force a transformation by whatever's accessing it which i DONT want in
this case, but DO want in #2

Then in #3 it only needs to know what stylesheet to use to process the xml..

Any advice? :/

thank you for any suggestions.

Jone