I have a small lan at home! ( 3PC + 1 Laptop )

Inviting some friends over this weekend so i decided to install some Lan game to entertain them!

They ask for "Diablo 2" so i am going to buy it later , but some of them told me that if i want to install it on all the 4 PC, i have to but all 4 sets of "Diablo 2".

Is that true?

i Dont really wish to buy that 4 sets of Diablo 2, cause i am really tight on budget?

Hmm.. Is there any other alternative to solve this Diablo2 Problem!