You could try Universal Access's Zoom feature. It allows you to Zoom into the screen with a key command and then the same key command takes you back to normal mode.
To use it, go to your Apple Menu and choose System preferences. In here, click on Universal Access and then note the Key Command for it. In mine it is OPTION - COMMAND (apple) - 8
There is also an Options button (in Leopard, maybe Tiger as well) and you can set different Zoom levels and other options like using the scroll wheel on a mouse.
Here are screen shots of my Pref Pane and the Options screen:
This should help you get that larger image when you need it and then zoom back out for normal work.
Hope this helps,
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