I'm currently using MSVC for C++ but as I'm switching to C to write a very performance-intensive program (interpreter) I have to search for a fitting C compiler.
I've looked at some binaries produced by Turbo-C and even if its old they seem pretty straigthforward and optimized.
Now I don't know what the best compiler for building an interpreter is, but maybe you can help me. I've considered GCC but as I don't know much about it, I can't be really sure.
99.9% a programs performance depends on the code you write and the language you choose. you can safely ignore the performance of the the compiler.
Stick to MSVC...and dont waste time :)
If you want a lightweight program, it is not the compiler you need to worry about so much as the code you write and the libraries you use. Most compilers will produce similar results from the same source code.
For example, using C++ with MFC, a basic windows application used to start off at about 900kB and grow rapidly. Linking with the dynamic MFC dlls would get you down to a few hundred kB. But by dropping MFC totally - using Win32 APIs directly - and using a minimal C runtime it was relatively easy to implement the same thing in an .exe of about 25kB or less (IIRC - it's been a long time since I did this).
So ditch the libraries and get back to proper low level C (or even C++ if you don't use too many "clever" features), and you can easily write very compact applications.
edit
I've just realised I was confused by the question title into talking about lightweight applications as opposed to concentrating on performance, which appears to be the real thrust of the question. If you want performance, then there is no specific need to use C, or move to a painful development environment - just write good, high performance code. Fundamentally this is about using the correct designs and algorithms and then profiling and optimising the resulting code to eliminate bottlenecks and inefficiencies. Note that these days you may achieve a much bugger bang for your buck by switching to a multithreaded approach than just concentrating on raw code optimisation - make sure you utilise the hardware well.
If I were you, I would take the approach of worrying less about the compiler and worrying more about your own code. Write the code for the interpreter in a reasonable way. Then, profile it, and optimize spots based on how much time they take. That is more likely to produce a performance benefit than using a particular compiler.
You can use GCC, through MingW, Eclipse CDT, or one of the other Windows ports. You can optimize for executable size, speed of resulting executable, or speed of compilation.
C++ was designed to be backward compatible with C. So any C++ compiler should be able to compile pure C. You might want to tell it that it's C and not C++, so compiler doesn't do name mangling, etc. If the compiler is very good with C++, it should be equally good, or better with C, because C is much simpler.
I would suggest sticking with MSVC. It's a very decent system. Though if you are not convinced - compare your options. Build the same program with multiple compilers, look at the assembly they produce, measure the resulting executable performance, etc.