Gpu with power supply

i just got my nvidia geforce gt 640 and it says i need a power supply with 350 watt and 20 amps on the +12 volt rail and the power supply in my computer is only 300 watt and im not sure about the +12 volt rail so would it be okay to use it in my computer for about two weeks or so till i can afford the new power supply?

what are the specs of your system?

  I do not know the specs of your system but I do know that under powering can be just as damaging to a system as overpowering a system. You might be alright if you do not over clock anything and only run one program at a time. Personally I would wait until I have the correct power supply. Two weeks is nothing compared to a damaged system component. I tend to play it safe rather than sorry. Now I could be wrong, and hopefully others will chime in with their advice too. Just my 2 cents worth.