How to use param value used as xpath in for-each for xslt

[eresh.leo]

I have a situation in xsl where I had a param value that will be assigned some where in xslt transformation. But I get that param as a String , that param may contains a node a unbounded[0 or more repetitions] . How can I use param in for each as just any other xml content as used by any xpath expression.

Here is my sample xmls: RetreiveData.xml

<soap-content>
------
<return>
<!--0 or more repetitions>-->
<data>
<startdate>12-12-12</startdate>
<enddate>12-12-13</enddate>
<nooftrans>5</nooftrans>
</data>
<data>
----
</data>

</soap=content>

This is my sample file which will be sent as param to xsl

xsl file:

<xsl style>
<param name ="retrieve"></param>
---
<xsl:for-each ="$retreive/return/data">
----do strufff
</xsl:for-each>

This was throwing an error . How can i travese to a node if it is param ?
I know this can be done using variable which is assigned to the path in a xml file . But that method is suggested in my scenario.

Can any one help me in solving this

Thanks in advance,
Eresh