On our links list, we link to an individual's free software which allows certain 'hobbled' Macs to use a true 'dual display', or spanning, setup.

He has posted an update for the program for Tiger users, available directly at this link:

Screen Spanning Doctor (Tiger) v.0.3.3

Basically, this program allows some models of iBook, eMac, and iMac to use a second display as a true second display, not simply mirroring the main display on the external screen. (These Macs are shipped as hobbled to help differentiate the need for PowerBooks, which have inbuilt spanning capability)

If disaster were to strike, and the video output was simply too much for the internal card to handle, it could blow the card. I wouldn't expect Apple to replace a blown video card (on those machines it's built on to the logic board, so the logic board would have to be replaced), but I haven't heard any horror stories about it yet, and have heard of a good number of people using it.

That said, it's always better to be aware of any issues, and the author has kindly provided a link to a forum topic on this discussion:

Screen Spanning Doctor Discussion