I think what Andy was trying to explain is that a POD published book is NO LONGER a new manuscript, WriteStuff. It was published -- whether it was published with Random House, or Del Ray or Aventine or PA. A NEW manuscript is one that hasn't been previously offered for sale to the public. If the public has had the opportunity to purchase the book, and hasn't so far bought thousands of copies of it, then there's an automatic strike against it to a publisher. They then must overcome the previous lack of sales and try to convince the public that it is now somehow a different, or better book.
Yes, it CAN be done, but it's difficult. It's much better to wait and find a publisher from the outset. If you have already published via POD, you can certainly give it a try, but it would be better for your purposes to downplay the sales to the public, rather than hype them. Don't LIE -- ever, but if sales weren't abnormally high, you can just tell an agent/editor that the book was only available in limited areas (like Amazon and the publisher's website), which might give them hope that a market still exists if they publish.
Does that make sense?