How to use Alpha layer for Docky ?

I succeed to do what I wanted, to make a transparent background :)

Edit : Is somebody knows if it's possible to add a Docky to AmiUpdate ?
Because, unlike a normal application, APPDIR:NetDock doesn't work.
Thank you

/**********************************************************
**
** The following function saves the variable name passed in
** 'varname' to the ENV(ARC) system so that the application
** can become AmiUpdate aware.
**
**********************************************************/
static void SetAmiUpdateENVVariable(CONST_STRPTR varname, CONST_STRPTR progpath )
{
/* AmiUpdate support code */
APTR oldwin = NULL;
TEXT varpath[1024] = "AppPaths";

/* stop any "Insert volume..." type requesters */
oldwin = IDOS->SetProcWindow((APTR)-1);

/*
finally set the variable to the
path the executable was run from
don't forget to supply the variable
name to suit your application
*/

IDOS->AddPart( varpath, varname, 1024);
IDOS->SetVar( varpath, progpath, -1, GVF_GLOBAL_ONLY|GVF_SAVE_VAR );

/* turn requesters back on */
IDOS->SetProcWindow( oldwin );

}

case DOCKYSET_FileName:
{
char buffer[LARGE_BUFFER];

IUtility->Strlcpy(buffer, (STRPTR)msgData, LARGE_BUFFER);
*(IDOS->FilePart(buffer)) = '\0';
SetAmiUpdateENVVariable("NetDock", buffer);

break;
}