just looking at jmeter, from what I can I see it is a desktop application, so is it safe to say I can use it to benchmark a windows server running asp.net?
any other rec
I recommend httperf from HP. As it just sends http requests it works regardless of the server you are testing on. You will need a linux machine to run it though. Another popular tool is Apache Benchmark (AB). I don't recommend it as the best tool available, but lots of benchmarks have been performed using this tool so it is easier to compare results and draw conclusions.
Microsoft offers various other tools for testing, but are not as widely used.