1. replace the string of zeros with your Google Account license key
2. add the full path to the googleapi.jar

The version of googlespell.bat that you installed looks like

@echo off
if x%1==x echo Usage %0 WORD-TO-SPELLCHECK GOOLGE-API-KEY
if x%1==x goto dun
if x%2==x %0 %1 00000000000000000000000000000000
del g.t
del googlespell.txt
@echo on
java -cp googleapi.jar 
             com.google.soap.search.GoogleAPIDemo %2 spell %1>g.t
@echo off
ren g.t googlespell.txt
type googlespell.txt
:dun

You need to change it to look like this (more or less):

@echo off
if x%1==x echo Usage %0 WORD-TO-SPELLCHECK
if x%1==x goto dun
if x%2==x %0 %1 qwertyuiopasdfghjklzxcvbnm23skdo
del g.t
del googlespell.txt
@echo on
java -cp c:\unicdocp\googleapi.jar 
             com.google.soap.search.GoogleAPIDemo %2 spell %1>g.t
@echo off
ren g.t googlespell.txt
type googlespell.txt
:dun

Of course, you will need to replace qwertyuiopasdfghjklzxcvbnm23skdo with your own Google Account license key and c:\unicdocp\ should be the folder where you installed UDP. But make these two changes in your copy and you can easily run googlespell.bat from any DOS box. Or on Win/NT/2K/XP, you can use the Windows Start > Run dialog and enter the following:

cmd /k googlespell [wordtocheck]

command /k googlespell [wordtocheck]