DataGrid validation of DataServices data - how??

Question

Hi, I'm trying to display data from WcfDataService (VS2010) in WPF DataGrid. Everything works. except of normal validation.
I was trying to make validation both with default WPF validation and IDataErrorInfo, but I can't get working all features I need. That is list of problems and questions:
1) How to disable DataGrid built-in check for convertion errors? Some values I'm trying to display and validate are not strings, so I even can't get value to validate - it will always be 0 or another default value. And I can't override error message to display in tooltip.
2) How to disable save button until validation errors exists?
3) How to make cell checking at startup, after editing, during typing together?
4) How to display tooltip for every cell, that is in error, not only for entire row (I want user to have an ability to see all errorrs when mouse over row "header" and to see personal error for single cell)?
Ohh, my head is going to blow :(