If anything make sure the drive is set to master on the jumper settings, though with only one drive you really shouldn't run into any problems. I think you can get away with a 60GB to 80GB possibly a 120GB

Seem that beyond the 120GB mark older macs require a Serial ATA PCI controller to recognize the storage size, either way a PCI card isn't an option on your iMac.

I installed a 60GB drive into a grape iMac 266MHz a little while back and aside from getting to the drive itself everything else went well.

 

I have 333 iMac and I put a 20 GB in there. Any normal sized IDE HD will fit in and work, but I think the disk controller will only recognize up to 120 GB.

One thing you should you know is that your system folder has to be in the first 8 gig's of your HD or the iMac won't find it. For example I have OS 8.6 on a 500mb partition, OS 9 on a 2GB and OS X on a 5GB partition and then a Documents partition for the rest of the 20GB.

 

Thanks for the speedy responses!

As always, I LOVE ehmac! (you are the guys that got me into the mac world in the first place!)

 

One thing you should you know is that your system folder has to be in the first 8 gig's of your HD or the iMac won't find it.

Huh? Are you sure? I don't think that's correct... the 8 GB limit applied the Beige G3 series and Mac OS X only.

 

Seem that beyond the 120GB mark older macs require a Serial ATA PCI controller to recognize the storage size

Not true, I don't believe. You don't need a PCI Serial ATA card to use hard drives bigger than 120 GB in size -- just a plain PCI ATA (100/133) card will do.