I am using my module adminhtml layout xml to add or remove tabs (you could use your theme's local.xml, based on these steps with a bit of tweakking.)
Firstly you will need to declare your layout updates (in your module config.xml) like the following:
<adminhtml>
<layout>
<updates>
<mymodule>
<file>mymodule.xml</file>
</mymodule>
</updates>
</layout>
</adminhtml>
Then in mymodule.xml, add the following (here, I am using the admin order view page handle)
<adminhtml_sales_order_view>
<reference name="sales_order_tabs">
<action method="removeTab">
<name>order_shipments</name>
</action>
<action method="addTabAfter">
<name>order_shipments_mymodule</name>
<block>mymodule/adminhtml_order_shipments</block>
<after>order_creditmemos</after>
</action>
<action method="addTab">
<name>order_receipts</name>
<block>mymoduled/adminhtml_order_recp</block>
</action>
</reference>
</adminhtml_sales_order_view
Hope this helps!! (Don't forget to upvote this solution)