You can, but the best way I know to do it, is to use WinAPI calls to set the window size etc before its created, then create it at the size etc that you need....
The header file "DarkGDK2.h" has 3 methods in it that can be used :
bool DarkGDKStart ( void );
void DarkGDKInit ( DWORD* pdwDisplayType, DWORD* pdwWidth, DWORD* pdwHeight, DWORD* pdwDepth, HINSTANCE* phInstance, LPSTR* ppApplicationName, HWND* ppParentHWND, DWORD* pdwInExStyle, DWORD* pdwInStyle);
int DarkGDKEnd ( void );
Personally i havent used them yet, but they are pretty self explanatory if you understand the winAPI.
The Advantage is that you have complete control over the program and its window through windows API, message pumps etc.. the Downside is that unless you are proficient in using the winAPI and C++ , its going to be a difficult task.
There are some tutorials however on using the Win32API with DarkGDK from before the above commands were added to DarkGDK. You can find them in these forums by searching "WinAPI tutorial".
If there is a simpler way of achieving what you want, I dont know it im sorry.
If it ain't broke.... DONT FIX IT !!!