I thought that cheat was for TS2?
TS3 is pretty easy to manipulate whether your sim has twins/triplets or not. I think you give them the fertility treatment, or have the mother listen to a lot of kids music/watch kids shows while pregnant. The family-oriented trait helps too I think.
I don't think I've ever used "forcetwins" in TS3; but combining the above works really well to get multiples.
Nah it was for TS3, it works fine on my neices' computer which has just the original TS3.