You can add a second menu and have it start somewhere other than the top level. For example, you could have it start with the current page and also show the children of the current page. Or, you could just show the children of the current page. Or you could do something else.
You did not say which version of DotNetNuke you are using. If you are using Version 6.x, you have the DDR Menu as the default menu and you can easily employ that in your skins. If you are using a 5.x version of DotNetNuke, you will need to get a copy of the DDR Menu from codeplex.com and install it in your DotNetNuke installation before you can use it.
There's excellent documentation for the DDR Menu at
http://www.dotnetnuke.com/Resources...uide.aspx. In particular, the NodeSelector attribute is used to determine where a menu starts and the depth of the pages it displays. You can use this together with IncludeNodes and ExcludeNodes to fine-tune the menu.
And, you can ask lots of questions here.
If you go to ainq.com and click the Company link, you will see several different navigation things happening in the left menu. This may be similar to what you want to do.