Do i need to upgrade my PSU to get a new video card?

the video card that im planning to get is ATI Radeon X1600 Pro / 512MB DDR2 / PCI Express / DVI / VGA / TV Out / Crossfire Ready / Video Card i've read that the card runs at 40 watts.my computer is a gateway GT5244E.it only has a 300 PSU,and i've done NUMEROUS calculations online and found out that... show more the video card that im planning to get is

ATI Radeon X1600 Pro / 512MB DDR2 / PCI Express / DVI / VGA / TV Out / Crossfire Ready / Video Card

i've read that the card runs at 40 watts.my computer is a gateway GT5244E.it only has a 300 PSU,and i've done NUMEROUS calculations online and found out that my computer runs BELOW 240 watts.so im thinking that the extra 40 watts from the video card is'nt gonna do harm right?the highest wattage that i got from a calculator is 240 watts,and the LOWEST wattage i got from a calculator is 214 Watts.so i should be okay with the upgrade right?
Update: scratch that highest wattage number.i forgot to add my PCI express 16X and then i calculated and the wattage went up to 295watts.. :/
Update 2: keep in mind that this is under the heaviest CPU load,for example start-up,so when my system is idle it should NOT go past 300watts
Update 3: i think i'll upgrade the PSU too just so i wont fry my computer LOL
Update 4: yeah ima upgrade it,which brand would you guys recommend?im planning on getting a 400 watter.
Update 5: thanks u.s soldier,and how do i know if a PSU will fit in my case?
Update 6: im planning on this one.

http://www.tigerdirect.com/applications/...
Update 7: first off venom i dont need 750 watts.thats overkill.and as for the card,im set on the one i chose.
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