Here are sample scripts to hide sections and tabs in CRM 4.0:
You need to specify a control id from the section:
//to hide section
After you find the ID of a tab, here is how to hide it:
//hide tab: tab1
crmForm.all.tab1Tab.style.display = "none"; //hide
There are lots of way to hide form elements. You can find a number of techniques by searching our blog for previous examples.