ITV Catchup is currently not a download service; it allows you to watch programmes online which aired up to 30 days previously. The service is sponsored (not supported) by Freeview i.e. they are advertising themselves.
ITV Catchup is a horribly user unfriendly service because being of a commercial nature you have to watch a handful of adverts before you get to the programme, with ad breaks mid programme also.
From next month BT Vision will include ITV Catchup as part of their service thus allowing their customers to watch shows minutes after they are originally aired on ITV, and for up to eight days after first broadcast.
http://www.itv.com/CatchUp/ITVCatchUpHelp/defa ult.html