How to use IF ELSE condition with XML by php?

Question

Hello guys.

I trying to make Blogspot.com like XML template engine with php. And I'm newbie in XML. How could make php script that read this type of XML and print out something to user's browser? I want to use too many free blogspot templates. Thank you.

....
<b:if cond='data:blog.con0'>
      blablabla1
            <b:if cond='data:blog.cond1'>
                  blabla3
                <b:else/>
                  blabla4
            </b:if>
      <b:else/>
      blablablabla2
</b:if>
....