if you are in the US, seeds are considered paraphenelia. The seeds may arrive with no problem (they usually do). The seeds may get held up by customs, in which case you will receive one of 2 letters - one that your package will not arrive - or one asking you to respond for more free seeds. If you respond then you are confirming that it was you who ordered seeds and you are screwed. The last possible scenerio is that you get hosed by the seed company who takes your money and sends nothing. I've seen dozens of posts on this site complaining about just about every seed company out there. Even the one I've "used" with much satisfaction has gotten some bad reps out here.
Do a google search of marijuana seeds and do the research yourself before you make a decision on which way to go. Make sure to keep in mind what you're looking for as far height, indoor/outdoor, ect before purchasing (if you go that route)