Use SuperDuper
Use SuperDuper! to clone the drive onto any external drive. It's free unless you want scheduling and smart backup options. I recommend purchasing it for those features. Carbon Copy Cloner would also work, but it had some incompatibilities with Tiger and Intel machines. SuperDuper is more reliable.
The 233Mhz iMac models didn't come with FireWire, so you will need an external USB drive enclosure compatible with an IDE hard drive. Be aware when ordering a hard drive that it must be IDE, not SATA. Cloning to and from a USB drive will be very slow because that model has USB 1.1, but it's basically your only option.
Also, the largest addressable drive on those machines is 128GB. You can use a larger drive like a 160GB, it just won't see more than 128GB of it. You will want a 7200rpm drive with at least 8MB or 16MB of cache. The 120GB and 160GB drives are very inexpensive now. If you're on a budget and don't think you'll ever need that kind of space you can of course save a few bucks and go with a 40GB or 80GB drive. More space is never a bad thing though. You can always partition the drive and use the other partitions as backups.
Max memory for that machine is unfortunately just 512MB (256MB x 2). It takes SO-DIMMs and I think you have to be careful about one of the slots which requires a low-profile module to fit.
A good place to order memory for any model Mac, usually cheaper than places like Crucial and guaranteed compatible, is OWC (
http://macsales.com). They also have hard drives, and if you find the various upgrades by searching for your specific Mac model it is difficult to order an incompatible upgrade. There are usually cheaper sources but most don't guarantee certified quality RAM, and Macs are very picky about RAM.
If you hang around eBay you may come across a Sonnet Harmoni FireWire upgrade kit for a decent price, which would open up many more possibilities for external storage, backups and CD/DVD burners.
Want to add wireless networking? Forget the Airport card or USB network adapters. Just get a D-Link DWL-730AP pocket router and put it in client mode. It acts like a wireless network adapter and plugs into your Mac's Ethernet port, so no software or drivers are necessary and it's only limited in speed by the 100Mbit Ethernet port rather than being limited to 802.11b speeds (Airport card) or USB 1.1 speeds (12Mbps). So if you have an 802.11g network you can get the full 54Mbps speed out of it even on that ancient Mac. The DWL-730AP costs around $50 most places. Try Cyberguys (
http://cyberguys.com).
Upgrading that machine to Tiger would work but performance would probably be terrible with just 512MB of RAM, so I wouldn't recommend it unless you have a specific need for running some piece of software that requires Tiger.
Find out more than you ever wanted to know by going through the articles, links and Mac Specs pages at Low End Mac (
http://lowendmac.com).
Have fun with your new Mac!
