Time keeps getting reset whenever I turn it off

[Ken Ihrig]

Whenever I turn my computer off, the time gets reset.  I assume that
the battery has gone bad.  Could someone please send me/post some info on
how to replace the battery i.e. are there any special things I need to 
do? any "tricks"? is there anyway to be sure that this is the problem
before replacing it?  Any info would be much appreciated.