Changing console font size.

Hi,

I'm making a simple console game (a snake clone) at the moment and would like to know why I'm having trouble changing the size of the font (or individual characters) from default to, say, 12x12.
I'm using SetCurrentConsoleFontEx and although I'm including windows.h, running Windows Vista (64 bit, if that makes a difference), and putting '#define _WIN32_WINNT 0x0500' at the top, it still is not compiling.
This function, SetCurrentConsoleFontEx, along with GetCurrentConsoleFontEx and CONSOLE_FONT_INFOEX are all undeclared.

Does anybody have any ideas?

Thanks.

(I hope this is the right forum for this topic)