出来ました。HDLのソースにヒントがありました。
;
; IEコンポーネントを使ったブラウザ
;
#define DIID_DWebBrowserEvents2 "{34A715A0-6587-11D0-924A-0020AFC7AC4D}"
#define DISPID_NAVIGATECOMPLETE2 252
#define OLECMDID_OPTICAL_ZOOM 63
cls 1
sdim url,512
url="http://hsp.tv/"
objsize 600,24
pos 0,2:mes "URL:"
pos 0,26:mes "WEB Browser Sample"
pos 40,0:input url
objsize 80,24
pos 560,24:button "移動",*wow
pos 480,24:button "進む",*go_f
pos 400,24:button "戻る",*go_b
////////////////ボタン追加////////////////
pos 160,24:button "縮小(50%)",*zoomdown
pos 240,24:button "通常(100%)",*normal
pos 320,24:button "拡大(200%)",*zoomup
////////////////以上////////////////
pos 0,48
axobj ie, "Shell.Explorer.2",640,480-48
num=stat
comevent ie_event, ie, "{34A715A0-6587-11D0-924A-0020AFC7AC4D}",*event ; DIID_DWebBrowserEvents2
ie->"Navigate" url
*main
stop
*event
; COMイベント処理
dispid = comevdisp(ie_event)
if dispid = DISPID_NAVIGATECOMPLETE2 : gosub *OnNavigateComplete2
return
*OnNavigateComplete2
name = ie("LocationURL")
objprm 0,name
pDoc = ie("Document")
name = pDoc("Title")
title name
delcom pDoc
return
*wow
ie->"Navigate" url
goto *main
*go_f
ie->"GoForward"
goto *main
*go_b
ie->"GoBack"
goto *main
*normal
zoom = 100 ; 100%
ie-> "ExecWB" OLECMDID_OPTICAL_ZOOM,0,zoom,0
goto *main
*zoomup
zoom = 200 ; 200%に拡大
ie-> "ExecWB" OLECMDID_OPTICAL_ZOOM,0,zoom,0
goto *main
*zoomdown
zoom = 50 ; 50%に縮小
ie-> "ExecWB" OLECMDID_OPTICAL_ZOOM,0,zoom,0
goto *main
解決です。