OK....what sort of tower is it? If it's a recent G4 or G5 tower it will most likely have a video card with two outputs on it. A DVI output and a ADC output. Also in the box should be a ADC->DVI adaptor. With these you can use two DVI TFT monitors. Alternatively with a DVI->ADC adaptor (extra cash) you could run two of Apples' old TFT monitors. (The old ones were ADC, the new ones are DVI). Or if you get hold of some DVI->VGA adaptors you could run two VGA monitors. The last option is not as good as the image quality is better with digital outputs-VGA is analog
EDIT: Having just checked the 2000 powermacs most likely it's one of these
PCI Graphics
or these
Gigabit Ethernet
If it's a gigabit ethernet it has DVI and ADC connectors. If it's a PCI graphics it's VGA only. Both have quite low spec G4 processors so you may like to consider a processor upgrade if you're going to be doing any serious video editing