[X-HW] Transferring OS X to a new hard drive

[techlists at comcast.net]

Hello,

I recently inherited an iMac running OS X (one of those one piece, round back, blue iMacs). The current hard drive is rather small, around 10 gigs, slow (I'm guessing 5400 rpm), and making clicking noises (so it might be getting ready to fizzle out on me soon).

I have a 20 gig, 7200 rpm drive that I'd like to stick in it, but don't have install CDs to re-install the OS. I have a USB external enclosure that I could stick the 20 gig drive in and plug the drive into the iMacs USB port. Is there a way to transfer the contents of the existing drive to the 20 gig drive, swap the drives, and have the new drive be bootable?

On another related note, is there any limitations on drive size that can go into this system? i.e. could I stick in a 30 or 40 gig drive if I had one available?

Thanks in advance,

Paul Greene