I feel like saying, no. No one computer language is required for a computer science student: programming is about algorithms and computer science is a sub-category of applied math.
Okay, now I have been a pedant, some recommendations. The first modern operating system, which wasn't supported by ONLY one vendor, was UNIX. These days we use the term both for some OSes and for a larger family of Unix and Unix-derived OSes which include Linux and Mac OS X. In fact, one can argue that Microsoft has used its monopoly power to try to suppress other OSes so badly, that they are faced with competition with one which is very important both to the infrastructure of the net and to academic computer science.
Pascal was created as a language to teach procedural programming with. A commercial version of it called Turbo Pascal made it incredibly popular among developers in the 1980's before C/C++ became accessible to Microcomputers and Java came along. It is STILL used at many schools to teach programming and is still quite good at allowing you to express computer concepts simply. Since I switched to Linux I haven't stopped using it, I've just switched to GPC which is a part of the GNU Compiler Collection. Here is a good free Pascal compiler though (yes it is available for my OS too):
http://www.freepascal.org/
I do not recommend C++ and Java as first programming languages -- for different reasons. I do recommend learning them. C is a procedural language like Pascal, except while Pascal mostly uses english like expressions like procedure and integer, C uses symbols like ? or & or abbreviations like printf for PRINT Format. Its creator has described C++ as C with namespaces and objects. I know several C++ programmers who have written excellent C code while denying they know the language. They are ignorant, perhaps but excellent programmers. Java is a cross-platform language which is useful for certain things. However you want languages like C++ C or pascal to do other things.
Perl and Python are good scripted languages which, like pascal are wonderful places to start. This is especially true as both have interpreters which allow you to enter commands and find out RIGHT NOW what effect they have, instead of waiting and having to hunt for whatever line of your program caused it to stop executing with a compiled program.
http://www.perl.org
http://www.python.org
My next suggestion is going to take in two concepts at once, so I'll go into the second here and the first, after. Lisp is a list processing language. If you ever played with Logo and with computer graphics when you were younger, that is derived from it. It is an entirely different paradigm of programming, and can be tough to wrap your head around, nevertheless it is extremely powerful, The Lisp Resource Kit is a Linux LiveCD which includes two books on Lisp, a lisp interpreter (Generally you use interpreters) running on Knoppix, which is a version of Linux which you never install. Linux is a great development environment -- regardless of what you have heard, it had graphical web browsers and a three dimensional environment like Aero before Windows did -- and their 3D environment, Compiz Fusion, uses MUCH less hardware):
http://common-lisp.net/project/lisp-res-kit/
I strongly recommend learning Linux or Unix if you are interested in computer science. I dislike Microsoft intensely. I do NOT recommend dumping Microsoft for any reason except that you WANT to. Knoppix, as I said, is a live cd. It was created as a portable desktop by a computer consultant named Klaus Knopper for use on house calls. In its unadulterated form it has C C++ and fortran compilers. In addition it has the interpreted languages perl, python, tcl/tk, bison and yacc. It has several text editors for entering programs (emacs and vi can function like IDEs but are so old they require a LOT of knowledge to use -- I started learning vi in 1989 and became confident in 2003). More information here:
http://www.knoppix.com
As for a site where you can learn how to do Flash, for most such tasks these days I suggest Youtube. People make videos about everything and with so many computers around you can assume computer-related tutorials are common there. So take a look:
http://www.youtube.com/results?search_type=&search_query=flash+tutorial&aq=f