HANDLE and DWORD variable types

These are not 'C' standard types.

Therefore, you need to look at the available data types in the C51 Manual and create your own suitable typedefs or #defines as required.

The same would apply for any other compiler.

Note that "DWORD" is a poor choice for a type name, as it gives no direct indication of its size or whether or not it is signed.
Hence I always prefer things like:
U8 - unsigned, 8 bits;
S16 - signed, 16 bits;
etc

These are not 'C' standard types.

Therefore, you need to look at the available data types in the C51 Manual and create your own suitable typedefs or #defines as required.

The same would apply for any other compiler.

Note that "DWORD" is a poor choice for a type name, as it gives no direct indication of its size or whether or not it is signed.
Hence I always prefer things like:
U8 - unsigned, 8 bits;
S16 - signed, 16 bits;
etc

Ah, you're trying to use the MS Windows API on an 8051, aren't you:

http://www.keil.com/forum/docs/thread7590.asp

That's a complete non-starter!