lbattraw, thanks for your response. I knew from another topic here that people used the Holux 236 with the 770, which is why I got that one. Well, that and the strong recommendation that it's a fine product.

I was thinking it could be set to sirf protocol (as I read on the net that some people had trouble getting it going), but then it should at least have given some response to the cat /dev/rfcomm0 command, or shouldn't it have?
And I was thinking it might be using a different channel...

In any case, I needed to check that Sirf vs NMEA setting, so I tried with a windows machine at work today - for lack of one at home, I have only Linux machines, including the N770 - and both with gpstool (I think that's the name) and sirfdemo from holux uk website, no data ever came out. I couldn't even connect to it, it seems.

That was whilst connected via usb.

Is it easy/straightforward to open it to short the internal battery, and would that void the warranty?

I passed the holux 236 to a colleague who has a bluetooth numerix device, and asked him if he could have a look if it would work for him; he might not be in tomorrow, so maybe I only get it back after the weekend, not sure.
In any case, I'm strongly thinking of sending it back.....