sharepoint provides a method called "commonShowModalDialog" which is used to show a popup window. i am on the popup window now, i need to redirect to another page within the popup window. is there any way to do that.
Or maybe SPUtility.Redirect() can help?
window.location.href = "URL"
inside the modal dialog; this will use the context of the open modal dialog to navigate to the new page.
Likely you want to steer away from this legacy approach to showing dialogs. If you are on SharePoint 2010 a better choice is to use the dialog API.
A good walkthrough can be found on MSDN Blogs at: http://blogs.msdn.com/b/jfrost/archive/2009/11/08/how-to-display-a-sharepoint-dialog-from-ribbon-button-and-get-selected-item-context.aspx