Changing the MacBook hard drive is very easy...instructions here.
You need a SATA 2.5-inch drive...here is a good list of some from a great Mac store. Drives currently max out at 200 GB, but not all manufacturers get quite that high. 160 GB is becoming a good high-end sweet spot. I prefer Seagate and Hitachi for drives.
The video shows how to take out the RAM and the hard drive. Remember to switch over the cover from the old drive to the new one. As for the size of the hard drive, I think Seagate has a 200 GB drive but it is only 4200 rpm.
Yep, 160GB is about the biggest they go. You *can* get a 200GB drive, but it runs at 4200rpm, which is pretty slow. I reccomend Hitachi. I've got a 160GB Hitachi in my Macbook and it is great.
The video shows how to take out the RAM and the hard drive. Remember to switch over the cover from the old drive to the new one. As for the size of the hard drive, I think Seagate has a 200 GB drive but it is only 4200 rpm.