This is something that I've thought about for a while but now as a friend is breaking a good 325i it has me thinking I might buy the diff and stick it in my 320d

What I don't quite know is:
Can I just bolt it up and driveron...
Is it any better than the crappy diff that I have I.e. Does it drive both wheels instead of just one....

And if it's not a runner is there another standard type of diff that fits the bill...

Thanks