Hi Woodman TA, I'm guessing from your shorthand that you only have one HDMI/DVI input on your system? If that's the case, to add an Apple TV and use the HDMI, you'll need an HDMI wireless switching box, say with four inputs and one output. Most are remote capable and some can 'learn' commands using IR.
If you have converted DVI to HDMI, you'll likely not have sound in the socket and need to use a separate sound cable. Try to use the optical output on the Apple TV---you may need a Toslink to SPDIF converter---as some of the latest HD movie rentals on iTunes can output Dolby 5.1 only through the Apple TV's HDMI output.
How do you get movie rentals in the UK? Got a friend in the US? ... ?
For TripEnglish, shame about the war ... bought your PS3 yet?