Magic :) lol jk. I dunno, it usually depends on which vamps ur on about. Various versions have different biology, hence different hypotheses on how one might impregnate another. Sorry I'm not more helpful.
Well "usually" the vamp controls the blood in his system and gets a hard-on LOL and apparently his swimmers don't die either so...baby coming! a girl vamp however cannot get pregnant...at least I've never read anything with that =P
because they are dead they can't become pregnant but in some stories like twilight they can and we don't become surprised because they are basically fiction charachters so everythings can happen in their life like pregnancy! even they're dead
If it is a male vampire with a female human. Yes , but difficult. At the moment of death-turning , the male still has a full tank of relevant bodily fluid. Obviously, when he finds a human female who he fancies and sleeps with her, he will de-tank, but unfortunately this is a one time event, as his body does not have the normal human hormonal creation system to refill the tank.It is a one try event unless of course they both opt for an invetro system in which case, a injection and cold storage method would be much more successful. they would of course have to discuss it with her parents and a independent counsellor, read all the leaflets and make an informed choice. It's all basic bats and the bees stuff.....