Hello.
I can only echo the previous two comments. There aren't "rumors" about sperm in pre-***. It's a medical fact. Prior to ejaculation, your body creates pre-*** to clean out the urethra. This fluid can contain millions of sperm left over from the last ejaculation. Sperm have been known to live up to 72 hours.
The average ejaculation contains 40-100 million sperm. But it only takes one active sperm and a few hundred helper sperm to create a pregnancy, so sometimes there may be more than enough sperm in pre-*** when sperm are present in it to make that happen.
Regarding sex during your partner's period: there's no reason to avoid it--but always use birth control because although it's rare, women can become pregnant during their period.
The two of you need to educate yourseves about pregnancy and STDs. See the MedHelp STD and birth control sites for more information, settle on an effective method, and play safe. Dr. J
If you do not want to get your girlfriend pregnant, please go to a Planned Parenthood clinic or any other clinic and obtain birth control such a the pill. If you do not want her on the pill, always wear a condom. If you are using the "timing" method for birth control and you are not aware that the rumor is true, you are going to become a father sooner than later. Good luck and take care of your life.
First question: Yes, the rumor is true -- if you don't wear a condom.
Second question: Depends whether conception is the goal or not.