How to determine a windows executables DLL dependencies programmatically?

That's not possible to determine. At least not without a whole lot of work. Any binary can call LoadLibrary to load a DLL. Even if you were to scan the code for all calls to LoadLibrary, you would have to determine what strings were being used to ID the library. Tracking down where in dynamic memory the string has been placed is going to be harder than you want to tackle.

76 lines to do that based on pedump code (don't forget to add Imagehlp.lib as dependancy):

#include <stdio.h>
#include "windows.h" //DONT REMOVE IT
#include "ImageHlp.h"
#include "stdafx.h"

template <class T> PIMAGE_SECTION_HEADER GetEnclosingSectionHeader(DWORD rva, T* pNTHeader) // 'T' == PIMAGE_NT_HEADERS 
{
    PIMAGE_SECTION_HEADER section = IMAGE_FIRST_SECTION(pNTHeader);
    unsigned i;

    for ( i=0; i < pNTHeader->FileHeader.NumberOfSections; i++, section++ )
    {
        // This 3 line idiocy is because Watcom's linker actually sets the
        // Misc.VirtualSize field to 0.  (!!! - Retards....!!!)
        DWORD size = section->Misc.VirtualSize;
        if ( 0 == size )
            size = section->SizeOfRawData;

        // Is the RVA within this section?
        if ( (rva >= section->VirtualAddress) && 
             (rva < (section->VirtualAddress + size)))
            return section;
    }

    return 0;
}

template <class T> LPVOID GetPtrFromRVA( DWORD rva, T* pNTHeader, PBYTE imageBase ) // 'T' = PIMAGE_NT_HEADERS 
{
    PIMAGE_SECTION_HEADER pSectionHdr;
    INT delta;

    pSectionHdr = GetEnclosingSectionHeader( rva, pNTHeader );
    if ( !pSectionHdr )
        return 0;

    delta = (INT)(pSectionHdr->VirtualAddress-pSectionHdr->PointerToRawData);
    return (PVOID) ( imageBase + rva - delta );
}


void DumpDllFromPath(wchar_t* path) {
    char name[300];
    wcstombs(name,path,300);

    PLOADED_IMAGE image=ImageLoad(name,0);

    if (image->FileHeader->OptionalHeader.NumberOfRvaAndSizes>=2) {
        PIMAGE_IMPORT_DESCRIPTOR importDesc=
            (PIMAGE_IMPORT_DESCRIPTOR)GetPtrFromRVA(
                image->FileHeader->OptionalHeader.DataDirectory[1].VirtualAddress,
                image->FileHeader,image->MappedAddress);
        while ( 1 )
        {
            // See if we've reached an empty IMAGE_IMPORT_DESCRIPTOR
            if ( (importDesc->TimeDateStamp==0 ) && (importDesc->Name==0) )
                break;

            printf("  %s\n", GetPtrFromRVA(importDesc->Name,
                                           image->FileHeader,
                                           image->MappedAddress) );
            importDesc++;
        }
    }
    ImageUnload(image);

}

//Pass exe or dll as argument 
int _tmain(int argc, _TCHAR* argv[])
{
    DumpDllFromPath(argv[1]);

    return 0;
}

In a nutshell, you need to scan the PE file's imports section for each DLL used by the executable. Then recursively locate and scan each dll until you've found all the dependencies.

Of course, apps can use the LoadLibrary family of functions for required or optional functionality. That won't be detected with this method.

Take a look at the IMAGE_LOAD_FUNCTION API. It will return a pointer to a LOADED_IMAGE structure, which you can use to access the various sections of a PE file.

You can find some articles that describe how the structures are laid out here, and here. You can download the source code for the articles here.

I think this should give you everything you need.

Update:

I just downloaded the source code for the article. If you open up EXEDUMP.CPP and take a look at DumpImportsSection it should have the code you need.