How can I Get one parameter in getCurrentPOSTData ?

The only way to do this would be to parse the POST parameters in a script. All of the parameters are delimited by an &, so you would

postArray = scrapeableFile.getCurrentPOSTData().split("&");
for (i=0; i
{
valPair = postArray[i].split("=");
key = valPair[0];
val = valPair[1];
if (key.equals("Desired text"))
{
session.log("Found it");
}
}