Sure. Basically, all you need are those two lines:
require "$sourcedir/ExtendedProfiles.pl";
$value = ext_get($username,"fieldname");
This will put the value of the field "fieldname" of the user $username into the variable $value.
To get this value from a SSI call, add something like this to your ExtendedProfiles.pl:
look for
1;
and add this before it:
sub ext_ssi {
print "Content-type: text/html\n\n";
print ext_get($username,"fieldname");
}
then open your SubList.pl and look for
%director=(
and add this behind it:
'ext_ssi',"ExtendedProfiles.pl&ext_ssi",
Now, you can use a call like
<!--#include virtual="./cgi-bin/yabb/YaBB.pl?action=ext_ssi" -->
which will display the value of the field "fieldname" for the user $username.