I bought the 8GB 70IT because I saw on another post that I could (probably) use a 500GB 2.5" external HDD providing I have a separate power source to power it. I have a micro-USB host cable, which seems to be working as I can use it to access some USB flash drives. I also already have a couple of Y-shaped USB cables.
So, I've tried connecting the HDD to my device, with only the power branch of the Y cable connected to my PC. But just about every time the Archos device thinks that it is connected to another host, and so asks if I want it to be mounted. I've tried connected every single piece in every possible combination of orders, rebooting the Archos device each time, but it always wants to be the client. Actually, not always. I did manage to get it to see the HDD as a HDD for about 30 seconds, then it went back to being a client
I'm pretty sure that my problem is that the extra power is telling the Archos device that it is connected to a PC, and so triggering client behaviour. I would be interested to know how to isolate that from the other end of the cable, as suggested previously.
I've contacted Archos support about this issue, they actually replied saying that they are "working on this issue". That sounds like they know that the device isn't acting as a host when users want it to, and maybe are going to be able to fix it. Perhaps a software fix to set host/client behaviour, rather than relying on what's plugged in?