First you have to pair the two devices together. If there is no link established, they will not communicate. Go to Settings > Wireless & network settings > Bluetooth settings > Check the box to turn on Bluetooth, and then make one device discoverable while you "Scan for devices" on the other device. You will have to enter the same paring code on each device...just use 0000 or 1234 (something simple). Then you should be able to send and receive files.
I've never actually paired my Archos 70 so I'm not sure if there are problems with this...but these instructions are pretty universal for most devices.