Is it possible to temporarily disable the screen timeout? Often, during updates/downloads or backup operations I would like to temporarily disable the screen time ( found under the 'menu - settings - Display - Screen timeout' ) without having to navigate to the above menu setting .

Anybody knows of a good widget which does just that : either disable the screen time ( by just clicking the widget ) , or by setting it to a high value / back to short value ( also by just clicking the widget ).

Or is there any other easy way I have missed ?

I am running Froyo on Samsung Galaxy S.
If you are using a profile application to set your volumes in different situations, I guest most of them have the option of changing your screen timeout as well. In my case I'm using Setting Profiles and I can add a new profile that does exactly that in two key press.

In Setting Profiles, there is a widget to set profiles and you can even select a timer with the profiles you set, for instance, to enable the profile "no screen timeout" for the next 5 minutes.