Ok, I found this:
"Although the Plug Computer USB connection can provide enough power for USB "thumb" drives, please do not expect it to power larger USB drives without an alternate power source. IT CAN handle the drives nicely through a powered usb hub. this makes the hub power the drive."
So it would be better to use a powered usb hub. Do you recommend any particular powered usb hub?
Also I found Excito B3 (https://www.excito.com/bubba/products/overview.html
) which has more or less the same specs as the SheevaPlug (1.2GHz ARM processor and 512MB RAM) but includes the hard disk, 2 USB, 2 Gigabit ethernet, 1 eSata.
It is more expensive than the SheevaPlug, and also is bigger (but includes a hard disk)... but do you know if it has overheating issues as well?
Thank you again.