I want to set up two web hosts, with fail-over, or even better fail-over and load balancing.

I can see how to do this using DNS (I'm familiar with zoneedit.com's services) and monitoring with a couple of local machines. I think the best I could hope for is a five to ten minute switch, and that's if my clients' DNS propogates quickly for them.

Is there a better way, perhaps using IP addresses instead? I've seen a little discussion about high availablity setups, but not much detail for me to go on.

Or is this something I could hire Linode support to set up with a couple of their servers (hopefully on separate generators)?

If both machines are on the same LAN, ideally right physically right next to each other, you can use IP address takeover. This is where the primary machine has the IP address, and the secondary monitors it. If the primary stops responding the secondary brings up an interface for the IP address ('takes it over') and does some ARP magic. When the old primary comes back on line it becomes the secondary.
The machines should have two connections (ethernet and null modem for example) to prevent a network error causing one to incorrectly think the other is down.
The switch time is something like 5 seconds.

Look at Heartbeat:
http://www.vergenet.net/linux/redundant_content/related/linux-ha/High-Availability-HOWTO-8.html
http://www.linux-ha.org/
At work we are looking at Zeus's ZXTM which is essentially a commercial version of hearbeat with dispatching, web gui, and other niceties.

As to whether this is something Linode would want to setup for you, I'm not sure. IMHO if your application requires that kind of availability you probably don't want a virtual server anyway.

Thanks, graham. I've gone through that website before, and it looks like something I'd like to try here within the office. It seems as if you need control (or at least background in) the network setup in order to make it work.

"IMHO if your application requires that kind of availability you probably don't want a virtual server anyway."

I'm not really looking for "high availability", just a way to automatically fail-over within 2-3 minutes without waiting for DNS to repropogate.

I'm looking now at http redirection and how that might help, or if it will confuse the web site visitors.

I have here the problem of my limited knowledge, and too many different technologies that might offer a solution.