I can't see Foley saving such a record, can you? So that leaves the page...or his parents. They could just copy and paste the whole chat to notepad.
If it were the parents, it does seem odd that they would have kept it under wraps. Parents tend to go after predators right away. Others in Washington might see such a chat bomb as a valuable chip to play later, whether for power or money. Soon all the rats will come out.
I'll bet that these pages are very politically connected partisans. What remains to be seen is whether the IM's are authentic or fabricated out of whole cloth. Maybe Mary Mapes has gone to ABC to break the story.