the stores recommending you buy new seeds each year is a ploy to get your money...mst seeds are good for at least 5 years (some 3-4) but if you store them in a cold dark place in a sealed container-ziplock baggy is fine or vac seal bag you can store them for much longer...saw a man had 25 year old tomato seeds that were viable

I just store mine in a tin. Based on what I have read, it is not the best way to do it but I have yet to have an issue.

Most seeds will store for a long time but your germination rates will drop. First year you might have 95% germinate - after a few years maybe 50-80% and eventually zero.
I found some tomato seeds that had to be 15 years old just in a paper envelope in the basement. About half worked.

anything I should watch out for when it comes to seeds??? someone once said something about seeds in that packs that have been changed so some plants wont produce seeds themselfs. any ideas or info on this??

http://www.amazon.ca/Seed-Saving-Techniques/dp/1882424581

This book will answer any and all questions on saving seeds..

With most hybrid plants(naturally crossbred) saving seeds is a bit of a crap shoot. The first generation of seeds(the ones you buy) will give you what you want. Save seeds from those and they may or may not begin to revert back to their parent stock.
Heirloom seeds are a new variety(all that crossbreeding figured out) and will reproduce true.

I bought my heirloom organic seeds from Hawthorn Farms and she told me all the seeds would last for 4-5 years except the onion seeds. They only last for the one year.

Heirloom seeds or even hybrids from self pollinators can be kept and should remain relatively true to form.(beans for example) However, related families like the brassicas, and squash/melon/cuc's can pollinate each other so if growing them in close proximity to each other you can expect hybrid offspring. Some brassicas are biennials so you could try letting some go to seed alternating years.
For storage, it's right that the germination rate will drop over time so just plan ahead and put one or two years seeds away. If necessary down the road and you need them, then bear in mind the cross pollination and only plant certain veggies a year or time them for blooming. But remember, seeds are living things. They do need air to survive. An envelope or non airtight container kept cool and dry will extend its storage time.