Photosmart 2570 scanner on LAN?

I have following problem:

HP Photosmart all in one was originaly installed with network cable
and one computer only. The printer choosed some own IP, assigned a
local IP address to my computer and both printing and scanning did
work.

Now however the connection is by adsl modem, and here DHCP sorce of IP
addresses is in operation.
The printer does still work, there is some tickbox in its driver panel
saying print to this printer even when IP changes.

Since there is no control panel for the scanner, I have no idea where
to set something, the scanner efuses to work, respectively is simply
not found by any application.

The scanner is in the list of devices (XP SP2), when clicking on the
button check scanner, all is reported fine.

It seems however that the twain system is not able to make contact to
the scanner somehow, since there no application now where I can scan
something from, even the HP own picture software is not able to
contact the scanner.

I tried to uninstall all drivers and install the 2570 with fixed IP
inside my netmask but outside of my DHCP range. I have set the IP in
the 2570 first.
But even after this the scanner was not found by any application, the
printer does work fine.

It seems that I can not use a fixed IP, nor DHCP range, but what then?
It looks like that when DHCP is present, the printer will get an
address from there and only ahen no dhcp is present in the net , th
eprinter will take his own defoult IP and then all will work again.
But how to operate the printer then in a net where all is connected
via the switch/router of the adsl modem which has the standard private
IP range 192.168.x.x in use?