Electrically, you are unlikely to have difficulties (but it will probably need an ATA/IDE drive not a SATA drive). The only difficulty you are likely to find is the depth of the drive - this can vary slightly. When faced with a similar problem a few years ago, I took the old drive out and measured it.

If you are not sure what to do, take the laptop into a computer shop. They should be able to replace the drive and transfer all the files across, but this will cost more than simply buying a bare drive on the internet.

Kaled.