Sorry - In my original post I said I was using an Ipaq 3680 - but it's not - it's a 3630.
It's running older ROM than you, too - Version 1.77.00 ENG, OS Version 3.0
The user manual does state that the Navman 3400 is only for Ipaq's 37XX and above, but i read a review in a GPS magazine of the 3400 where they only had a 3630 in the office and it was working fine.... so I took the risk and it's paid off - so far.
The Navman manual also says not to use IBM micro-drives for the maps - due to current requirments and the like, but I've ignored that too and no problems. Been using the Navman every day since 28th December, and it's not fried yet! Though it might happen any day now....
John