Spurs are willing to let one of Chiriches and Kaboul leave the club, but the price for Chiriches might be a little higher because of his age, and also because the Romanian is the second choice right back now so he has more value to Tottenham. If the price scared Roma off of him, they may be able to snag Kaboul for less.
If Kaboul did join Roma, it would be on a loan with an option to buy in the summer. There is no word yet on what that price to buy him in the summer would be.
Kaboul has played just twice in the league since November and is clearly not in Mauricio Pochettino's plans. He may be the captain, but he's about out of the team now and the 29-year-old would like to go somewhere that he will play. He may not play at Roma, but he would have a better chance there than at Spurs, so that might be the deal that gets him away from White Hart Lane.