Hey Jon,
Well if you want to check if you PSU can handle your GPU you need to check how much watt your are using with the new setup. there are several calculators for this. (eg: http://www.extreme.outervision.com/psucalculatorlite.jsp). Just compare whatever value rolls out with what you have. What you should also check is that your CPU won't bottleneck if you install a new card.