Just change
<company_onepagecheckout before="IWD_OnepageCheckout">Company_OnepageCheckout</company_onepagecheckout>
to
<Company_OnepageCheckout before="IWD_OnepageCheckout">Company_OnepageCheckout</Company_OnepageCheckout>
If it is not working then used
<global>
<!-- This rewrite rule could be added to the database instead -->
<rewrite>
<!-- This is an identifier for your rewrite that should be unique -->
<!-- THIS IS THE CLASSNAME IN YOUR OWN CONTROLLER -->
<mynamespace_mymodule_onepage_iwd>
<from><![CDATA[#^/onepagecheckout/index/#]]></from>
<!--
- mymodule matches the router frontname below
- checkout_cart matches the path to your controller
Considering the router below, "/mymodule/checkout_car/" will be
"translated" to "/MyNameSpace/MyModule/controllers/Checkout/CartController.php" (?)
-->
<to>/comonepagecheckout/index/</to>
</mynamespace_mymodule_onepage_iwd>
</rewrite>
</global>
<frontend>
<routers>
<comonepagecheckout>
<!-- should be set to "admin" when overloading admin stuff (?) -->
<use>standard</use>
<args>
<module>Company_OnepageCheckout</module>
<!-- This is used when "catching" the rewrite above -->
<frontName>comonepagecheckout</frontName>
</args>
</comonepagecheckout>
</routers>
</frontend>
See more at