Most seeds will be viable for at least a few years if stored properly. Best is a cool, dry, dark place. There's a how-to from Rodale's Organic Life at: http://www.rodalesorganiclife.com/garden/top-10-tips-storing-seeds. I don't get nearly that fussy about it, but still have good results. There are also some charts online showing how many years different kinds of seeds can be expected to last.

To do a germination/viability test on questionable seeds, put a few (about 10) seeds on a moist paper towel in a baggie, seal it up, then set it in a dark place for a few to several days. You'll soon see whether the seeds are still viable and what percentage.

Thanks for the help :)