Well, replacing the Hard Drive isn't all that difficult.
Transferring the data on the other hand, can be.
The least expensive is backing up all your data onto DVD's, and then transferring that onto the new hard drive, you also may need a new Windows disc.
Another option is transferring your data to an external Hard Drive, and then putting the data onto the new hard drive.
Another option is cloning your drive, but I don't have experience with it.