diff -Nur orig/src/dos/dos.cpp new/src/dos/dos.cpp
--- orig/src/dos/dos.cpp	2009-09-13 19:28:36.000000000 +0200
+++ new/src/dos/dos.cpp	2010-11-07 17:22:48.000000000 +0100
@@ -890,11 +890,25 @@
 			}
 			break;
 		}
-	case 0x5c:			/* FLOCK File region locking */
+	case 0x5c:			/* FLOCK File region locking */
+		/* ert, 20100711: Locking extensions */
+		Bit32u pos=(reg_cx<<16) + reg_dx;
+		Bit32u size=(reg_si<<16) + reg_di;
+		//LOG_MSG("LockFile: BX=%d, AL=%d, POS=%d, size=%d", reg_bx, reg_al, pos, size);
+		if (DOS_LockFile(reg_bx,reg_al,pos, size)) {
+			reg_ax=0;
+			CALLBACK_SCF(false);
+		} else {
+			reg_ax=dos.errorcode;
+			CALLBACK_SCF(true);
+		}
+		break;
+		/*
 		DOS_SetError(DOSERR_FUNCTION_NUMBER_INVALID);
 		reg_ax = dos.errorcode;
 		CALLBACK_SCF(true);
-		break;
+		break;
+		*/
 	case 0x5d:					/* Network Functions */
 		if(reg_al == 0x06) {
 			SegSet16(ds,DOS_SDA_SEG);
diff -Nur orig/src/dos/dos_files.cpp new/src/dos/dos_files.cpp
--- orig/src/dos/dos_files.cpp	2009-09-13 19:28:36.000000000 +0200
+++ new/src/dos/dos_files.cpp	2010-11-07 15:36:12.000000000 +0100
@@ -402,6 +402,20 @@
 	};
 	return Files[handle]->Seek(pos,type);
 }
+
+/* ert, 20100711: Locking extensions */
+bool DOS_LockFile(Bit16u entry,Bit8u mode,Bit32u pos,Bit32u size) {
+	Bit32u handle=RealHandle(entry);
+	if (handle>=DOS_FILES) {
+		DOS_SetError(DOSERR_INVALID_HANDLE);
+		return false;
+	};
+	if (!Files[handle] || !Files[handle]->IsOpen()) {
+		DOS_SetError(DOSERR_INVALID_HANDLE);
+		return false;
+	};
+	return Files[handle]->LockFile(mode,pos,size);
+}
 
 bool DOS_CloseFile(Bit16u entry) {
 	Bit32u handle=RealHandle(entry);
diff -Nur orig/src/dos/dos_misc.cpp new/src/dos/dos_misc.cpp
--- orig/src/dos/dos_misc.cpp	2009-05-27 12:15:42.000000000 +0200
+++ new/src/dos/dos_misc.cpp	2010-11-07 22:12:48.000000000 +0100
@@ -58,7 +58,11 @@
 }
 
 static bool DOS_MultiplexFunctions(void) {
-	switch (reg_ax) {
+	switch (reg_ax) {
+	/* ert, 20100711: Locking extensions */
+	case 0x1000:	/* SHARE.EXE installation check */
+		reg_ax=0xffff; /* Pretend that share.exe is installed.. Of course it's a bloody LIE! */
+		break;
 	case 0x1216:	/* GET ADDRESS OF SYSTEM FILE TABLE ENTRY */
 		// reg_bx is a system file table entry, should coincide with
 		// the file handle so just use that
diff -Nur orig/src/dos/drive_local.cpp new/src/dos/drive_local.cpp
--- orig/src/dos/drive_local.cpp	2009-07-18 21:42:56.000000000 +0200
+++ new/src/dos/drive_local.cpp	2010-11-07 23:12:00.000000000 +0100
@@ -37,7 +37,8 @@
 	bool Read(Bit8u * data,Bit16u * size);
 	bool Write(Bit8u * data,Bit16u * size);
 	bool Seek(Bit32u * pos,Bit32u type);
-	bool Close();
+	bool Close();
+	bool LockFile(Bit8u mode, Bit32u pos, Bit16u size);
 	Bit16u GetInformation(void);
 	bool UpdateDateTimeFromHost(void);   
 	void FlagReadOnlyMedium(void);
@@ -466,7 +467,50 @@
 		*size=(Bit16u)fwrite(data,1,*size,fhandle);
 		return true;
     }
-}
+}
+
+/* ert, 20100711: Locking extensions */
+#ifdef WIN32
+#include <sys/locking.h>
+bool localFile::LockFile(Bit8u mode, Bit32u pos, Bit16u size) {
+	HANDLE hFile = (HANDLE)_get_osfhandle(_fileno(fhandle));
+	BOOL bRet;
+
+	switch (mode)
+	{
+	case 0: bRet = ::LockFile (hFile, pos, 0, size, 0); break;
+	case 1: bRet = ::UnlockFile(hFile, pos, 0, size, 0); break;
+	default: 
+		DOS_SetError(DOSERR_FUNCTION_NUMBER_INVALID);
+		return false;
+	}
+	//LOG_MSG("::LockFile %s", name);
+
+	if (!bRet)
+	{
+		switch (GetLastError())
+		{
+		case ERROR_ACCESS_DENIED:
+		case ERROR_LOCK_VIOLATION:
+		case ERROR_NETWORK_ACCESS_DENIED:
+		case ERROR_DRIVE_LOCKED:
+		case ERROR_SEEK_ON_DEVICE:
+		case ERROR_NOT_LOCKED:
+		case ERROR_LOCK_FAILED:
+			DOS_SetError(0x21);
+			break;
+		case ERROR_INVALID_HANDLE:
+			DOS_SetError(DOSERR_INVALID_HANDLE);
+			break;
+		case ERROR_INVALID_FUNCTION:
+		default:
+			DOS_SetError(DOSERR_FUNCTION_NUMBER_INVALID);
+			break;
+		}
+	}
+	return bRet;
+}
+#endif
 
 bool localFile::Seek(Bit32u * pos,Bit32u type) {
 	int seektype;
diff -Nur orig/include/dos_inc.h new/include/dos_inc.h
--- orig/include/dos_inc.h	2009-09-13 19:28:32.000000000 +0200
+++ new/include/dos_inc.h	2010-11-07 15:03:22.000000000 +0100
@@ -112,7 +112,9 @@
 void DOS_SetupFiles (void);
 bool DOS_ReadFile(Bit16u handle,Bit8u * data,Bit16u * amount);
 bool DOS_WriteFile(Bit16u handle,Bit8u * data,Bit16u * amount);
-bool DOS_SeekFile(Bit16u handle,Bit32u * pos,Bit32u type);
+bool DOS_SeekFile(Bit16u handle,Bit32u * pos,Bit32u type);
+/* ert, 20100711: Locking extensions */
+bool DOS_LockFile(Bit16u entry,Bit8u mode,Bit32u pos,Bit32u size);
 bool DOS_CloseFile(Bit16u handle);
 bool DOS_FlushFile(Bit16u handle);
 bool DOS_DuplicateEntry(Bit16u entry,Bit16u * newentry);
diff -Nur orig/include/dos_system.h new/include/dos_system.h
--- orig/include/dos_system.h	2009-03-04 22:08:22.000000000 +0100
+++ new/include/dos_system.h	2010-11-07 15:12:12.000000000 +0100
@@ -70,7 +70,9 @@
 	virtual bool	Read(Bit8u * data,Bit16u * size)=0;
 	virtual bool	Write(Bit8u * data,Bit16u * size)=0;
 	virtual bool	Seek(Bit32u * pos,Bit32u type)=0;
-	virtual bool	Close()=0;
+	virtual bool	Close()=0;
+	/* ert, 20100711: Locking extensions */
+	virtual bool    LockFile(Bit8u mode, Bit32u pos, Bit16u size) { return false; };
 	virtual Bit16u	GetInformation(void)=0;
 	virtual void	SetName(const char* _name)	{ if (name) delete[] name; name = new char[strlen(_name)+1]; strcpy(name,_name); }
 	virtual char*	GetName(void)				{ return name; };