can a 16x graphic card slot able to support 8x 128mb graphics card?
http://www.gigabyte.com.tw/Support/M...ProductID=1796

and wats the minimium voltage for the psu to support a Intel P4 530 3.0Ghz
with this mobo

That board only takes PCI_E X16 graphics cards.

An AGP 8X would not fit.

As to the other question do you mean the minimum Wattage or do you actually want to know Voltage?

its better to let me know the minimum wattage n the actual voltage..
thank you

Wattage and amp needed depends on how much RAM you have, how many and which fans, IDE's i.e HDD, CD drive, DVD drive, SATA's, peripherals- PCI etc cards, AGP cards, you have. Without anything fancy but two hard drives, a CDRW and a DVRW, with one fan I've stably and comfortably managed using a 150W PSU for this with a P4.

Go to the link in my sig and click on the Power Supply Calculator link in General PC & Repairs. Choose everything there and add about 25% on top and see whats recommended power needed.