You don't need to upgrade to a more powerful PSU for the GT 430. It gets all its power from the PCIe slot, and that slot is spec'd to provide 75W. While it's always better to have more PSU than you need, you can still use your existing PSU for that card.
Here is a PSU calculator for future PSU upgrading: http://www.thermaltake.outervision.com/
Yes. And here's another thing... if you do ever have more card than your PSU can power, you will simply experience a re-boot or a shut down when the PSU can't keep the voltages up to spec. Aggravating, but not something that will do damage.