I can get the script working as follows:

#!/bin/sh
for name in `ls *.rtf`
do
name1=` echo $name| cut -f 1 -d . `
mv $name1.rtf $name1.doc
done

is working fine, but how do I make it work like this:

chext 1 2

where 1 is the original extension and 2 is the desire new extension?