Donna, I am not sure this is true and there is at least disagreement among Canon Lawyers and priests on this subject. Some would argue that if you are civilally divorced but the marriage is not anulled by the Church that any beahvior you engage with someone of the opposite sex for romantic purposes that would not be permitted while you were still legally married would be considered adultery. Therefore you would not be permitted to recieve communion until going to confession.
Brian, you are correct. Since the Church assumes all marriages are sacramental unless proven otherwise, a person who is civilly divorced without a decree of nullity and is romantically involved is taking a huge risk in possibly committing adultery and at the very least, is causing scandal. A divorced couple may, in fact, not have a sacramental bond but that cannot be determined unless one of the spouses goes through the annulment process.
I know this sounds harsh, but it is the truth. The problem is we have lots of priests out there who, after hearing the circumstances of someone's divorce, they will encourage them to go ahead and date because they believe there are viable grounds for annulment. The very good, solid priest who counseled me after my divorce told me exactly that. But I found out the hard way that's very risky business.
The best way to ensure one's ability to receive the sacraments after divorce/before annulment is to have social relationships only. Not romantic.