Vista RTM using TV as secondary display problems

I've just upgraded my HP Compaq Presarion M2000 notebook from XP Pro to Vista
Ultimate RTM, and updated the drivers for all the bits of hardware where I've
been able to find them. Now, when connect my TV to the laptop using the
S-Video connector, successfully detect the TV (sometimes I have to go into
the ATI Catalyst Control Centre and say force TV to be detected), then use
fn-F4 to clone the laptops lcd display to the tv, I get nothing: i.e. both
displays switched off; constant switching between the two displays,: i.e. the
laptop displays for a couple of seconds then goes black, then the TV displays
for a couple of seconds, and so on until I get a migraine; or the laptop
display goes blank and the TV displays the desktop but at too high a
resolution so that text is barely legible (running the Media Centre in Vista
works well though) and in all three cases it is impossible to get back to
having the laptops LCD being the only display. I've tried using the ATI
Control panel to set the LCD as the primary display and disable the TV, but
applying those changes doesn't work - it always goes back to the TV as the
primary display and the LCD disabled - and I've tried enabling the laptop's
display and disabling the TV through the windows control panel, but the same
problem occurs: applying the changes doesn't work. I've tried using Vistas
built in wizards for connecting to an external display, and the ATI wizards
for the connecting, but neither method produces a stable state. The only way
to get the laptop display up and running is to power down the laptop using
the hardware switch (shutdown and restart from the start menu don't work -
see my other post), unplug the S-video and restart the laptop.

Can anyone suggest any way of getting this working? All I want is to be able
to use the TV as a clone display so that I can use the Media Centre, and be
able to disconnect the laptop from the TV and carry on using it without
having to do a cold reboot.

Thanks