I have a 3month old rottie/collie cross and was thinking of getting a dobermann pup.  Would like to know what the best way to introduce them would be?

Personally I would wait until your current pup is grown and well-trained before you introduce another one.

Couldn't agree more JG :)

As the others have said wait at least another 18 months to two years.  You will need that amount of time to train yoiur current puppy, it needs your undivided attentionb.

Also having two close in age is more likely to cause issues regarding status.