I have an XML document that contains XPATH references like the
following:

<ROOT>
  <DATAID>1</DATAID>
  <DATAS>
    <DATA>
      <ID>1</ID>
      <TYPE>Type1</TYPE>
    </DATA>
    <DATA>
      <ID>2</ID>
      <TYPE>Type2</TYPE>
    </DATA>
  </DATAS>
  <DATA reference="/ROOT/DATAS/DATA[1]/ID" />
</ROOT>

In my XSLT, I need to be able to acquire the /ROOT/DATA/@reference
string and then using some type of evaluation extension, I need to be
able to obtain the value pointed to by the XPATH of this attribute.
Therefore, the select result would yield '1'.

I've read I could use XALAN-J or EXSLT; however I am unclear how to:

1. Install these extensions in my web application
2. Reference them for use in my XSLT.

Can someone give me a quick and dirty step-by-step of how to do this?

Chris