link failure - undefined references to graphical functions

I have working C++/Windows program compiled with Visual Studio 2008. The program consists of just two .cpp files. I am now attempting to compile and link it using MinGW. So far I have successfully compiled both source files without error, but now when I link them with the command...

g++ -o program.exe file1.o file2.o

... I get many instances of "undefined reference to.." assorted graphics related functions like:

GetStockObject, SelectObject, MoveTo, LineTo, SetPixel, TextOut, BitBlt, CreatePen etc.

I am not getting undefined references for any other types of windows call. Clearly I have missed something in my linker command line, but cant work out what.