Apple TV cannot record anything; it only downloads movies and TV shows from iTunes or shows Youtube stuff.
The Archos TV Plus, I'm pretty sure, will work like a Tivo, that is, it will come with an infrared device that you put on your SKY receiver/decryption box so the Archos can tell the SKY box to change channels at the appropriate time, and then record a show from the same feed that goes in to your television.
The archos is also supposed to allow internet surfing and (like the Apple TV) download programs from the internet as well.
if you're only using SKY (and not a DVB-T source like Freeview), and if you already have a Sky+ and/or HD box, then the TV+ will not offer any additional features to your current set up.
Sky encrypts most of it's content and it can only be de-crypted by a Sky receiver, this means you can only record programs from one of the SKy outputs, at the moment this has to be an analogue source which will degrade the quality of picture you get, so I wouldn't bother.
This will be the same for any similar device (e.g. Apple TV)