Unfortunately the Masked Edit text box went away with VS.NET.
It will reappear in VS 2005 and is available with third party controls (e.g. Infragistics).

All that aside, a possible way to do this is to handle a text box event when you want the validtion to occur (e.g. KeyPress, Leave, LostFocus, ModifiedChanged, TextChanged, Validated, Validating) with a regular expression validation (or ,even better, perhaps call a MM.NET rules object that contains a regular expression validation routine - if that is able to be done in MM.NET).
The Regular Expression checks the controls text value for an acceptable "Matching" pattern (numbers in your example). Good tool to help with RegEx http://www.regexbuddy.com/index.html

Alternatively you could code something like the following in the textbox's KeyPress event handler:
if( !char.IsNumber(e.KeyChar) & (Keys)e.KeyChar != Keys.Back & e.KeyChar != '.' )
{
e.Handled= true;
}

Another option would be to use WinForms validator controls. See the following for more details: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnadvnet/html/vbnet04082003.asp

Lastly, if this is a common scenario, create a custom control that inherits from mmTextBox class and adds input validation functions, required validation functions and MaskEdit.
An example is found at: http://www.codeproject.com/vb/net/validtext3.asp