easy
the windows op sys has been able to accomodate multiple monitors since win 98 zand the card manufacturers have become much more adept at allowing multiple cards to coexist
the best way i have found is to purchase 2 cards from the same company not req to be the same
personally i use a radeon AIW(all in wonder) 9600 and a radeon 9200
gives me 2 monitors or monitor tv from the AIW
and a second monitor from the 9200
but remember the second card must be a pci card
(no computer i know of has 2 agp slots (design limits)
previous to the radeons i used a vodoo3 pci and a generic 8meg agp vid card
its just a matter of installing the card physically windows should do the rest without problems
only one issue the cmos sometimes has a setting allowing to set either pci slot or agp slot as primary video graphics best to make sure thts set for your present card primary before install that way new card doesnt act like replacement for present card (meaning reinstall old drivers too
)