Tools to develop .net application( Web application)?

Any version of Visual Studio starting, perhaps, from 2005 and later. Free-of-charge Visual Studio Express is also good enough.

Please see:
http://en.wikipedia.org/wiki/Visual_Studio[^],
http://www.microsoft.com/visualstudio/en-us[^],
http://en.wikipedia.org/wiki/Visual_Studio_Express[^],
http://www.microsoft.com/express/Windows/[^].

Alternatively, you can use Open Source SharpDevelop on Windows or MonoDevelop on Windows and Linux (yes, you can do .NET and ASP.NET development on Linus and a number of other OS, please see Mono). Please see:
http://en.wikipedia.org/wiki/SharpDevelop[^],
http://sharpdevelop.com/[^],
http://en.wikipedia.org/wiki/MonoDevelop[^],
http://monodevelop.com/[^],
http://en.wikipedia.org/wiki/Mono_(software)[^],
http://www.mono-project.com/[^].

Basically, this is all you need. I also advise some open-source tools to work with graphics:

Inkspace (Windows, Mac OS X, Unix-like):
http://en.wikipedia.org/wiki/Inkscape[^],
http://www.inkscape.org/[^];

GIMP (Windows, Mac OS X, Unix-like and more):
http://en.wikipedia.org/wiki/GIMP[^],
http://www.gimp.org/[^].

I would strongly recommend to create and post-process all graphics in external tools, not in Visual Studio or other IDE.

—SA