(1) Does ASP .NET run on UNIX?
**They have mono, but once they complete it .net will be on the next version so I would say if you do .net you go with an IIS server.
(2) Does ASP .NET worthy to learn?
**Yes, it is very similar to Java so and since you are a C guy they have C# so it is really not hard to learn.
(3) IS there a way to compare PHP with ASP .NET
**Lots of sites compare to the two. They both have advantages and disadvantages.
(4)I have programmed in PHP a little bit and trying to learn web programming in depth in one direction.
**If you really want to get into web development you should really know how to code in them all. IMHO, They are all so similar that it is really not that bad. As long as you know C and VB syntax the programming world is your oyster.