I can give you a couple of tips…
First of all, try some masturbation sessions where you prevent yourself from reaching an orgasm. Basicly, masturbate untill you think you’re about to come, and stop. wait a couple of minutes, and go at it again. This is a great way to know where your limit is. This exercise wont actually prevent you from ejaculating, but you’ll know early when you’re about to.
Second, know what happend when you come. When you’re heavily exited and about to ejaculate your PC muscle tends to spasm (the part between your balls and your ass if you need to go technical). If you dont want to ejaculate, try to relax that part. “Kegels” will help you achieving this, but in the end, it is all a matter of trying it (just concentrate next time you masturbate, you’ll notice these contractions if you pay attention).
Third, CHILL OUT. I remember my first couple of encounters, and I was so anxious I totaly screwed it up. Not getting an erection has probably nothing to do with you physically (although one never can be sure). Look at it this way: sex is supposed to be fun. If you’re going to stress out about getting an erection, it is not going to be fun. Take your time, be sure to do a lot of foreplay, and if the erection doesn’t come, then it doesn’t come. Big deal, women don’t feel like it on command either ;)
I personally dont believe you should stop masturbating, but just don’t do it 5 times a day. Masturbate to find things out: what do you like? What turns you on? What makes you lose control? Dont forget to enjoy it though, because otherwise the purpose is kind of lost…
Let us know how it works out.