How to notify user of invalid data grid entry?

[Horus Alkebulan]

I have a data grid that uses the Edit, Cancel, Update features.

However, I haven't come up with an easy way to notify user if data they've
entered is invalid (i.e. too long, wrong type, etc.)?

Can you bind the controls that appear when you click Edit to a Validator? If
so how?

Or can you add text somewhere conspicuous that the user will see it that
displays the problem.

Please provide code if possible. I'm using VB but can do a pretty good job
of translating C# to VB. I'm slightly above novice ASP.NET programmer as I
do have working data bound pages.

Thanks

Horus