max hard drive size in an original MacBook

I am posting here to get some information out that I had a a hard time finding for myself when hard drive shopping.

I have an original launch MacBook that I wanted to upgrade the hard drive on for the second time. The last time I did this, I called up Apple support and asked them what the biggest drive I could install was. Their answer was "120GB" so that is what I bought and it worked well for quite some time, but eventually got a bit cramped. So I decided to throw caution to the wind and pick up a 5400 RPM Seagate 320 GB hard drive that I got for an amazing deal.

So I slap that bad boy in, boot to my Tiger disk and format it with the disk utility. I then proceeded to do the Time Machine backup, but the drive was not shown.

Panic sets in.

After taking a few deep breaths, I rebooted, once again booting to my Tiger disk, and guess what? The drive showed up and I restored my time machine backup onto the new drive in about 4 to 5 hours.

Lesson learned: A 1st gen MacBook will support a 320 Gig drive as long as it is the right form factor/interface.

That's great, that the original MacBook will take any size depending on the form factor/interface. But what's the proper form-factor/interface that got you 320 GB? It didn't work the first time, but did the second? What did you change?