It's never okay to have sex w/o a condom ... if you want to protect yourselves against pregnancy and STD's.
In fact, if her cycle is regulated at all (which i'm guessing it's not, since it takes about 5 years to do so), 14 days would be approx the middle of her cycle, when she's most likely ovulating. (Note: This is not written in stone by any means, and all girls are different. Having sex when you believe you're not ovulating doesn't mean there's no risk. Always be careful and use condoms if you want to avoid pregnancy)
I think both of you may want to do some reading and learn how reproductive systems work, especially your gf. But good on you for coming here and asking questions Now you know ...
Here are some articles to start w/;
Pregnancy Risk Flow Chart
Safer Sex Primer
On the Rag
"He who asks a question is a fool for five minutes; he who does not ask a question remains a fool forever."
[This message has been edited by LilBlueSmurf (edited 07-02-2002).]