Regular expressions enable QuickTest to identify objects 
and text strings with varying values.

You can use regular expressions when defining the 
properties of an object, the methods of an argument, when 
parameterizing a step, and when creating checkpoints with 
varying values.

A regular expression is a string that specifies a complex 
search phrase. By using special characters such as a period 
(.), asterisk (*), caret (^), and brackets ([ ]), you 
define the conditions of the search.

we can write the user defined in a notepad and save the 
file as .vbs and we then associate that to Test-Settings-
Resources-Associate Library Files by clicking plus and 
select the .vbs file.  In the script we can call the 
function with function name ()

Uday is exactly correct.........

I m giving one example 4 regular exp.........
  [1-9]--------->it accepts all 1 to 9 numbers......