if you drag and drop a textbox on a form  the max size is standard 32767
characters  , however AFAIK you can set it to the integers datatypes max size

FROM MSDN :

In code, you can set the value of the Text property to a value that has a
length greater than the value specified by the MaxLength property. This
property only affects text entered into the control at run time.


Windows NT 4.0, Windows 2000, Windows 2000 Professional, Windows 2000
Server, Windows 2000 Advanced Server, Windows XP Home Edition, Windows XP
Professional x64 Edition, Windows Server 2003 Platform Note: For single line
text box controls, if the MaxLength property is set to 0, the maximum number
of characters the user can enter is 2147483646 or an amount based on
available memory, whichever is smaller. For multiline text box controls, the
maximum number of characters the user can enter is 4294967295 or an amount
based on available memory, whichever is smaller.

Windows Millennium Edition Platform Note: For single line text box controls,
if the MaxLength property is set to 0, the maximum number of characters the
user can enter is 32,766 or an amount based on available memory, whichever is
smaller. For multiline text box controls, the maximum number of characters
the user can enter is 65,535 or an amount based on available memory,
whichever is smaller.

HTH

Michel