According to http://www.cyberhome-help.de/tadl528_english.php4 you can`t turn Macrovision off.
If you look in the 528 forums on that site, there is a link to a Macrovision hack, but if you visit here http://www.sector101.fsnet.co.uk/cyberhome/ you will see it is a bit scary.
Either wait until someone works out the firmware (if possible, of course), or try www.sonel.com for a device which in their words
"This ingenious scart to scart video stabiliser eliminates Flashing Pictures, Colour Drop Out, Brightness Fluctuation, Muted Screen Symptoms and other protection interference etc." (Macrovision to you and me) - £29.99 inc P&P. Other people here have said how well it works.
R