Okay, so you have a form on, lets say..
sourcefile.asp which displays to the browser this link code..
<A HREF="destination.php?IDnum=8880">Link</A>
now if destination.php look like this, it will use that value passed to it..
<FORM METHOD=POST ACTION=nextfile.php>
<INPUT TYPE="HIDDEN" NAME="IDFromASP" VALUE="<? echo $IDnum; ?>">
<INPUT TYPE="SUBMIT" VALUE="Submit this form">
</FORM>
and for the file that destination.php submits to, have this..
<?
echo "Your ID is: $IDFromASP";
?>
Is that what you wanted?