Pff, lots of noise about nothing. For 100! just use your computer:

Code
  
pepin@bombast:~ % python
Python 2.3.5 (#1, Aug 19 2006, 21:31:42) 
[GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

>>> result = 1
>>> for i in range(1,101):
...     result *= i
... 
>>> 
>>> result
93326215443944152681699238856266700490715968264381621468592963895217599993229915
608941463976156518286253697920827223758251185210916864000000000000000000000000L
>>>