The code looks like it should work, you will want to ensure that it appears after the validation toolkit code on the page or it may not work correctly. I changed it up just slightly for you, I removed the unneeded quotes and broke the calls into multiple lines like this:
<script type="text/javascript">
WAValidateRQ(document.forms[0].partgroup,'- Entry is required',document.forms[0].partgroup,0,true,'checkbox');
WAValidateEN(document.forms[0].partgroup,document.forms[0].group_code,true);
WAValidateRQ(document.forms[0].partgroup,'- Entry is required',document.forms[0].partgroup,0,true,'checkbox');
</script>
Reading over your original post again though I'm not sure if you would need all of this code in the onload event to make it work properly. You may be able to get away with some much simpler code on the page. What is the problem with the way the page loads currently? If you are just trying to make one of the form elements disabled or enabled by default this can be done with some code like this:
<script type="text/javascript">
document.forms[0].group_code.disabled=true
</script>
This would make the group_code element disabled when the page loads. If you want to make the element enabled by default you could set this to false instead of true.
