In which forum should I ask Dymo-Costar related questions?
Forum: Printers from other manufacturers 
How do I set the resolution?
Use the pbm2lwxl tools. Set resolution to 300dpi.
How do I make this printer work with USB?
You need to make a small modification to the USB driver. These
steps were reported working.
1. Unpack linux-2.4.20
2. Change to /path/to/src/linux-2.4.20/drivers/usb
3. Edit printer.c
4. About line 880, there's the detection code. There's a check to see
if the transfer type is 'bulk'. I just commented out this check. Note
that according to the USB spec that I read, the 315 violates the usb
if ((epd->bmAttributes&USB_ENDPOINT_XFERTYPE_MASK)!= USB_ENDPOINT_XFER_BULK) continue;
/*if ((epd->bmAttributes&USB_ENDPOINT_XFERTYPE_MASK)!= USB_ENDPOINT_XFER_BULK) continue; */
5. Configure/compile as usual.
What are the known problems?
There are some white lines in some output. Barcodes worked fine,
the text below showed some white lines. It should be fine for labels.