hi
I'm looking for a window form textbox allowing to insert just floating point values, with 3 decimals.
I remember that in VB6 there was a property called data member witch was doing it.

Is there in C# something like that?

Could you suggest to me a tutorial or an HOWTO?

Thanks in advance! :)

My cheap $0.02:
I think you have two options.

1~ Validation of complete text in the text box.
Say you have the textbox tBox_1, and you will use whatever the user enters there when they click on button btn_1. Then, in the handler of the Click on btn_1 I'd perform the validation before doing anything else:
string s = tBox_1.Text;
bool b = isValidFloatingPoint(s);
if(!b)
  //Report issue via MessageBox or throw an Exception
//Do whatever you need to do.

2~ Intercept and handle the ChangedValue event of the tBox:
this even is triggered every time the text in the tBox is changed (such as when the user
enters a new value, or appends something).

I don't have much experience with the second option, since I usually end up using the first one.
Look at any chapter on Events and Delegates for mor einfo.
Also, you may look at the Regex class to quickly check if the input is a valid floating point.

HTH,
Olorin