pci is abt 133mbps
agp 1x is double
similiary go one
approx ask others is all this is right
if you wanna buy graphic card try to avoid all this
geforce ,geforce 2 ,geforce 3 (though geforce 3 ti 500 may support majority games atleast it is too old and no need to buy it now ,besides who will sell it),geforce 4 (though 4 ti is not that bad but still go for newer cards),geforce fx,radeon 8500 series or lower,radeon 7xxx series,radeon 8xxx series,radeon 9550 series,radeon 9200series,radeon 9000series,any radeon 'se' graphic card,
if you wanna buy :
geforce 6 series(depending upon requirement if you don't want to game 6200 is ok for running os,photoshop shd be fine etc)
try to avoid nvidia turbo cache(tc) and ati hypermemory
try to avoid ati if they don't give more performance than their equivalent performing nvidia cards as of now that is
try to avoid X300 series,X600 series,X700 series