Problem solved!
Solution to puzzle 3
1. ... Qxe7??
brutally leads to checkmate in four moves:
2. Qxe4+ Kb8
3. Qb6+ Bb7
4. Nc6+ Ka8
5. Qa7 mate.
This must rate as one of the most fascinating chess games ever played, with Kasparov repeatedly setting such deadly traps for the unfortunate Mr Topalov, right until the seemingly inexorable conclusion!