It should be possible for you to replace your modem. You don't say which type it is, but I am asuming it is internal (not an external USB modem.)
You would buy a modem card (probably a PCI card), open up your PC swap the old modem card for your new one and install any nessesary drivers which would come with your new PCI card.
You can buy surge protectors for both power sockets and phone sockets. I have a 4 socket extension lead which had surge protection built in. It also has two phone sockets on it. It wasn't expensive. This would probably protect your PC from electrical surges caused by electrical storms.
Robert
November 2005