Setting my changes back for prompt.c.  Greatlord and I agreed about this.  These was a miscommication about these changes and the way different MS version handle it.

Modified: trunk/reactos/subsys/system/cmd/prompt.c

--- trunk/reactos/subsys/system/cmd/prompt.c	2005-09-03 11:50:23 UTC (rev 17619)
+++ trunk/reactos/subsys/system/cmd/prompt.c	2005-09-03 11:51:22 UTC (rev 17620)
@@ -204,12 +204,20 @@

 		return 0;
 	}
 

+	/* if it is null, then it needs to set to default,
+	   because that means the user entered "prompt" only.
+		so even if param is null you _must_ still set prompt
+		to the default.  There seems to be some kinda difference 
+		between winxp and 2k in this matter and this way will 
+		cover both. */
+	if (param[0] != _T('\0'))
+		_tcscpy(szParam,param);
+	else
+		_tcscpy(szParam,_T("$P$G"));
+

 	/* set PROMPT environment variable */

-	if (param[0] != _T('\0'))
-	{
-		if (!SetEnvironmentVariable (_T("PROMPT"), param))
-		    return 1;		
-	}

+	if (!SetEnvironmentVariable (_T("PROMPT"), szParam))
+		return 1;

 			
 	return 0;
 }