You need a 450w psu with 26amps on the 12v rail. You should be just fine.
A link to your actual psu would be great to make 100% sure but unless you have a real bad one you will have enough juice.
where are you buying the card from and for how much? you might be able to get a better card for the same amount.
38a on the 12v rail so your psu will be just fine.
Take a peek at this card:
Newegg.com - XFX GS250XYDFC GeForce GTS 250 512MB Core Edition 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Desktop Graphics / Video Cards