var how_many_ads = 4;
var now = new Date();
var sec = now.getSeconds();
var num = sec % how_many_ads;
var ad_content=new Array(); 

ad_content[0] ='<table width=948 border=0><tbody><tr><td><A HREF=http://list.6park.com/parks/out.php?perm=vodgo.com target=_blank><img src=http://am.6park.com/img/vodgo/vodgo.gif WIDTH=468 HEIGHT=60 BORDER=0></A></td><td><IFRAME FRAMEBORDER=NO SCROLLING=NO SRC=http://list.6park.com/local.php?which=bbspost468&adnum=no1 width=468 height=60></IFRAME></td></tr></tbody></table>'

ad_content[1] ='<table width=948 border=0><tbody><tr><td><A HREF=http://list.6park.com/parks/out.php?perm=uncnhome1 target=_blank><img src=http://img.6park.com/img/uncnhome1/46860.gif WIDTH=468 HEIGHT=60 BORDER=0></A></td><td><IFRAME FRAMEBORDER=NO SCROLLING=NO SRC=http://list.6park.com/local.php?which=bbspost468&adnum=no2 width=468 height=60></IFRAME></td></tr></tbody></table>'

ad_content[2] ='<table width=948 border=0><tbody><tr><td><A HREF=http://list.6park.com/parks/out.php?perm=liyi99 target=_blank><img src=http://img.6park.com/img/liyi99/46860.gif WIDTH=468 HEIGHT=60 BORDER=0></A></td><td><IFRAME FRAMEBORDER=NO SCROLLING=NO SRC=http://list.6park.com/local.php?which=bbspost468&adnum=no3 width=468 height=60></IFRAME></td></tr></tbody></table>'

ad_content[3] ='<table width=948 border=0><tbody><tr><td><a href=http://list.6park.com/parks/out.php?perm=0086card target=_blank><img src=http://img.6park.com/img/0086card/46860.gif WIDTH=468 height=60 border=0></a></td><td><IFRAME FRAMEBORDER=NO SCROLLING=NO SRC=http://list.6park.com/local.php?which=bbspost468&adnum=no4 width=468 height=60></IFRAME></td></tr></tbody></table>'

document.write( ad_content[num]  )