Hi Sujith,
I've used one alternative to IIS for .net before. It is called Abyss Web Server and it's good, at least for my requirements then.
You can check it out here at http://www.aprelium.com. This runs on Windows.
You can also run .net using Mono. I've not used this before. You can try it out. The site is http://www.mono-project.com.
If you're not in a rush, wait for Mono 2.0. This can be run on multiple platforms.