As long as the Laptop is relatively new, then you wont harm it by putting in bad RAM.
It will beep as Kentaree said, but it will do so in a specific manner, which you should be able to decifer via the manual that came with the motherboard ( or alternatively, the home page ), which will tell you what's wrong.
For example,
short beep - short beep - long beep - repeat
could mean that an AGP ( or equivelant ) card may only be partially inserted, etc etc.
Hopefully this will help.
Jess.
Team EOD :: Programmer/Logical Engineer/All-Round Nice Guy