What the AP said is true however I think it is worth mentioning that "windows" specific isn't the only hurdle. There are compiler issues to worry about as well.

Since we don't have any code to go on I can't begin to guess if you have or have not included "Windows specific" code. Some simple things to check for would be including the windows.h header, using macros or functions defined in windows.h. To find out just comment out the include windows.h line and see if it still compiles.

If you want to check if have included compiler specific statements which are also possible given some of the Visual Studio based tutorials out there you could try using DevC++/Code Blocks with mingw.

Other than the items above and maybe a few more the only real way to find out is to try to compile on another platform and compiler such as Linux and gcc and see what happens. I have had some pretty good success compiling SDL applications on different versions of fedora core however there are many different flavors of Linux such as Mandrake, ubuntu, knopix etc. Take a look here for more information on different linux distributions.

Hope it helps.

Sorry if I am a bit un-clear - long day and it looks OK so far :)