I got it working. Here is the source of a window.

forward
global type w_main from window
end type
type lb_files from listbox within w_main
end type
type cb_cancel from commandbutton within w_main
end type
end forward

global type w_main from window
integer width = 3305
integer height = 1844
boolean titlebar = true
string title = "Drag Files"
boolean controlmenu = true
long backcolor = 67108864
string icon = "AppIcon!"
boolean center = true
lb_files lb_files
cb_cancel cb_cancel
end type
global w_main w_main

type prototypes
Subroutine DragAcceptFiles(Long hWnd, Boolean fAccept) Library "shell32.dll"
Function ULong DragQueryFile(Long hDrop, ULong iFile, Ref String lpszFile, ULong cch) Library "shell32.dll" Alias For "DragQueryFileW"

end prototypes
on w_main.create
this.lb_files=create lb_files
this.cb_cancel=create cb_cancel
this.Control[]={this.lb_files,&
this.cb_cancel}
end on

on w_main.destroy
destroy(this.lb_files)
destroy(this.cb_cancel)
end on

event open;// Enable Drag Accept Files
DragAcceptFiles(Handle(lb_files), True)

end event

event close;// Disable Drag Accept Files
DragAcceptFiles(Handle(lb_files), False)

end event

type lb_files from listbox within w_main
event wm_dropfiles pbm_dropfiles
integer x = 37
integer y = 32
integer width = 3186
integer height = 1508
integer taborder = 10
integer textsize = -8
integer weight = 400
fontcharset fontcharset = ansi!
fontpitch fontpitch = variable!
fontfamily fontfamily = swiss!
string facename = "Tahoma"
long textcolor = 33554432
boolean vscrollbar = true
boolean sorted = false
borderstyle borderstyle = stylelowered!
end type

event wm_dropfiles;// WM_DROPFILES

Constant ULong FILECOUNT = 4294967295
ULong lul_size = 260, lul_index, lul_chars, lul_idx, lul_max
String ls_FileName

lul_max = DragQueryFile(handle, FILECOUNT, ls_FileName, lul_size)

For lul_idx = 1 To lul_max
	lul_index = lul_idx - 1
	ls_FileName = Space(lul_size)
	lul_chars = DragQueryFile(handle, lul_index, ls_FileName, lul_size)
	lb_files.AddItem(ls_FileName)
Next

end event

type cb_cancel from commandbutton within w_main
integer x = 2889
integer y = 1600
integer width = 334
integer height = 100
integer taborder = 10
integer textsize = -8
integer weight = 400
fontcharset fontcharset = ansi!
fontpitch fontpitch = variable!
fontfamily fontfamily = swiss!
string facename = "Tahoma"
string text = "Cancel"
boolean cancel = true
end type

event clicked;Close(Parent)

end event