IIS Load

How much load the front end webserver can handle.

This has to do with your server's processor speed, memory, and pages being served.
In addition to that, what I consider one of the best features of iis is the ability to manage how much bandwidth a site can use.
If more traffic is coming into the server, you can use another webserver and use load balancing to ease the load on the primary webserver.
As far as concurrent connections, it's hardware dependent.
HTH

"Load Balancing" is mainly for CPU balancing, it doesn't do much help as far as network speeds go.

But it depends on what you're hosting and how popular it is. If you're serving static files, then your internet trunk speed is the most important factor.

If you're serving dynamic stuff like PHP or ASP, then CPU and RAM are very important, but also HDD speeds if you've got a database server.

For compiled webapps, like ASP.NET, the CPU thing isn't as important, but you need more ram to compensate for the CLR and additional worker processes.

Note that "bandwidth limiting" for IIS requires QOS be installed.

also note, that if the web server is Win2K Pro the limit is 10 concurrent users. otherwise, no limit (in theory) on the amount of visitors online in the same time.

Windows XP's IIS5.1 has that limit too.