Custom tags and attributes

Hello.

I need to use custom tags and attributes on my web pages, just to  
store and use some data via javascript (I don’t allow to create this  
tags at runtime too). All I know is that XHTML allows Namespaces  
usage, but in this case page doesn’t pass validation on W3C site. I  
can’t find any methods to solve my problem to use custom attrs and  
keep code valid. Could you advice me something? Thank in advance.

Andrew Marcus.