that probably wont work out so well. rather, it might work, but youll get the random crashes if it runs at all, and risk damaging your other components.
It might mean delaying the upgrade until you have some more money, but i would recommend that you get an antec or corsair power supply of 450 - 550 watts.
this guide should also give you an idea of some other good specific models of psu's that the forums knows of.
*READ FIRST* Updated Power supply guide
you may also want to consider saving up for a new system, with yours starting to get dated. the upgrade now shouldnt be a problem, as any future system can reuse the power supply.