jdawg - Sperm Wars is a book, so I doubt you'll be able to find a link to the whole thing. I found it on amazon here for you, but you can probably save a lot of money by just going to the local library - I bet they have it somewhere.
http://www.amazon.com/Sperm-Wars-In...bs_sr_1?ie=UTF8&s=books&qid=1201062928&sr=8-1
Your body can tell the difference between your hand and an actual vagina for starters. I don't know the science behind it, but since reading Sperm Wars, I've come to realize the human body is a freakishly advanced piece of hardware. Consider this - your body knows just how much sperm to inseminate into your partner every time you have sex with her. The term they use is 'topping off', basically you will ejaculate only the needed amount of semen to be most effective. If you haven't had sex with a girl for a week you'll likely blow a full load of around 600 million sperm (more or less). If you just got done having sex 30 minutes ago you will only blow 50 million.
Another thing to consider, which doesn't come from the book just my experience, we as males know how to turn ourselves on. We know what would feel good, etc.. When you're with a female she may make sudden moves, get you in uncomfortable positions, and a whole host of other things that may prolong your ejaculation. On the other hand, the first time your penis encounters a real vagina - it will probably be only a matter of minutes. Further, you'll be involved emotionally, you'll feel her warmth, she'll be moaning, etc... all these things will drive you to the edge. The main point here is that there are tons of differences. However, it is impossible to actually set out to list these discrepancies and on top of it all describing them is nowhere near as fun as experiencing them. So good luck to you and have fun!