Office 2003 and 2010 working alongside each other

Hi,

If I have a thinapped version of both Office 2003 and Office 2010 streaming to a desktop how does it decide which default version to use? (i.e. when opening a Word document from explorer), so far I have found it will use Office 2010 as default but I have one user which has defaulted to using Office 2003.

Regards,

Ross