serial connection with "Usb to 1s 1p" converter

I have an Usb-to-1-serial-and-1-parallel port converter, and I want to
use it to connect my beagle revC4 to my host pc. Unfortunately, I
cannot get any output in minicom when I power the board.
I have set up the device to /dev/ttyS0 in minicom first, with no luck.
But watching the dmesg output, I've seen that ubuntu creates a
/dev/ttyACM0 device when the board is powered, so I tryed with this.
But I cannot run minicom with this device set before the board has
been powered, because this causes minicom to exit with a "no such file
or device" error. The problem is that if I run minicom after the
beagle has been powered, I get no message from the board.
The usb-to-serial hub is recognized by ubuntu, but no device node is
created. I also tryed to manually create a device node for the hub
through an udev rule based on the vendorId and productId (I can obtain
them using lsusb), but when I try to use such device node in minicom,
I obtain the error "No such device or address".
I tryed connecting the beagle to another old pc with a built-in serial
port, and it runs well using /dev/ttyS0 (i.e. the beagle init messages
are displayed correctly).
But I cannot use such old pc for all the development, so I need to
make my hub work. Can anyone help me?
Thank you very much in advance.