DataGrids don't do what your saying. With a DataGrid it knows it is going to be bound to a single table/view/sproc and you build all of the fields for editing and all of the code for submission.
The first problem with this method:
How does your table know what the primary key is?
Second problem:
Are you going to output textboxes for everything or will you have some mechanism for knowing that you need a dropdown for some values?
Third Problem:
How are you going to have users enter data for records that are foreign keys to other tables?
Fourth problem:
How does they system know when to hide certain fields? Or will everything be displayed and all of it in plain text? (think password fields, email, etc)
I was going to draw up an example of how you could do it, but I couldn't let myself. You couldn't do this all in one table editing page with a DataGrid without a great deal of code behind it. I don't think it's a good idea to do it in ASP 3.0 either.
Basically you will not want to do this unless you are doing a bunch of schema queries behind the scenes to help you determine field types, keys, relationships, etc. We build seperate database editing pages because the end user needs the context we give them, need the dropdowns, validation, hints, fields descriptions, etc. Otherwise tey woudl be doing your job and you would be off bulding the next phpMyAdmin.
-T