|If your computer came with a hard drive larger than 137GB then it is 48 bit LBA compliant. That means that any size hard drive sold will work.|
Just be aware that there are two interface types IDE ATA & SATA. You must have the proper connections to use either.
If you have the room there is no reason to replace the hard drive. You can simply add a second hard drive and have even more space. Below is a link showing both types. Compare the connections to what you have available on the motherboard.
Below is an excellent place to buy hardware. Note that a bare drive means no screws or cables.