how can i execute a REG_EXPAND_SZ command ?

[ohadp]

I'm implementing my own version of the Explorer 'New' menu. 'Create Shortcut' and 'Create Briefcase' are both stored in the registry as REG_EXPAND_SZ strings. I've used ExpandEnvironmentStrings to translate things like %SystemRoot% to c:\winnt\system32. My problem is the %1, %2 parameters. I've succesfully ran the 'create shortcut' command supplying the directory under-which I want the shortcut to be created in instead of %1. When I try to play the same trick on the Briefcase item it does nothing. What does the !d! in : %SystemRoot%\system32\rundll32.exe %SystemRoot%\system32\syncui.dll,Briefcase_Create %2!d! %1 translate to ? What are the rules for %1 %2 and %x ? Is there a 'normal' way to execute this commands, without hacks ? Thanks