YES, if the RAM is not compatible with the motherboard, you can ruin both the RAM & the Motherboard.

No, it will not ruin a thing but if the screen does not turn on and the comp. doesn't start correctly then simply take out the stick of ram and your old ram and your MOBO will work fine i gurantee it 100% ok! !

Be sure to have Sterlin pay for your new motherboard and RAM then...  There are different sizes of memory with different amounts of pins and so forth.  If you try to force a module that's too big/small into your motherboard, you can permanently damage your motherboard.  I guess if you're bent on trying it, the safest thing to do is count the pins on the module that's in your computer and compare those on the new memory.  If the number matches, you can try it, but I wouldn't hold my breath.

ok so i guess i was lucky when i put the wrong MHZ ram in my dimension and it worked by simply replacing the ram with the old again. THANKS FOR THE INFO I KNOW NOW THAT'S NOT A GOOD WAY OF TESTING IT LOL.

I was going to go there, but you beat me to it.  Very well said.  I can't count how many motherboard's customers kill motherboards with the right ram, no less the wrong ram.

thanks for the responses. any suggestions on finding out what kind of RAM this is then? it doesnt say anywhere on it.

Does it have a part number on it?  If so, try doing a Google search on the part number and see what turns up.

Your best bet would be to find out what computer your friend took it out of.  Make sure to (if it's a Dell) get the model number, processor type and speed, and the speed of the front side bus speed.  Then let us know what you're running.  We should be able to tell you if it'll work or not that way.