Screen refresh rate

I am trying to connect a Dell Inspiron 6400 to an external screen. Hardware:

The Laptop is Core Duo T2400, upgraded to have Radeon 256MB X1400 mobility
graphics
External screen is Iiyama Vision Master Pro 454.
Laptop has drivers for the screen and it appears in my device manager with
the correct Iiyama name, along with 3 other Default monitor entries. I don't
know what these are! I only have the Iiyama and the laptop's own screen.

I have pressed the key combination on the laptop to get the picture to the
external screen only and I have the laptop lid shut. Problem is that I can't
change the refresh rate away from 60Hz and it is giving me a headache!

Display Properties->Settings->Advanced->Adapter->List All Modes and nothing
over 60Hz is listed!

Ideally I would like the external screen to be my main screen (1600x1200 @
85Hz) with the Start menu and I would like the internal laptop screen to be
a secondary display for help systems and web pages etc (1600x1050 or
thereabouts!!)

What can I do?

Thanks

I'd go to the sites of both the monitor and card's manufacturer, download
and install the latest/greatest drivers for each of them, and see if there's
any support options on their sites, that could provide insight.

sa