  just wanted to get everyone's attention. this was going to just go in the comments section since if you haven't read ziks' post: "wheel in the sky keeps on turning", you will be totally lost. however, it got really long and i feel math should always make the main page. so ziks, close, young skywalker. starting hands, check. there are indeed 10810 ways of getting 2 cards to a straight flush...of a particular suit. gotta multiply by 4 to cover all of the options. luckily in the world of probablility almost everything is multiplied so we can do that at the end. 4 * (10810/270725) * (946/1533939) is 9.8501e^-5 but wait, what about this scenario:AD, 2D, AS, 2S then you have 2 chances to get the straight flush from the board. there are (5 c 2) times (5 c 2) ways to get this stroke of luck given 2 specific suits. since it matters not what 2 suits are paired, we can multiply this by (4 c 2).
so this is 10 * 10 * 6. we can plug that 600 into the system to get (600/270725) * (946/1533939) * 2(twice as many chances to complete the flush) = 2.7336e^-6 of course, before adding remember that we already covered 1/2 of these 600 options earlier so divide by 2 first. final probability: 2.7336e^-6 + 9.8501e^-5 = 101.2346e^-6 this yields .01012346% of course that number doesn't mean too much since you never go into a hand looking for a straight flush of that calibur.
the 946/1533939 (.06%) is the one that you should think about when choosing to bet to the sky in hopes of catching it on the river or whatever it is in omaha. of course it's up to .12% if you have a double draw. time to get the deed to the house! as far as your other concern, as long as the cards are face down and no one else can change the 5 cards that get dealt to the board, it doesn't matter where you sit or the number of people. it's like saying what are the odds of getting the ace of spades after i take one face down. you can either look at it as "what's the probability of card 2 being the ace of spades," or the long way: prob of you getting it if i have it plus prob of you getting it if i dont have it.
if i do, 0% + if i dont (51/52 * 1/51) or 1/52. this type of thing happens on a much greater level than i have time to explain at the poker table. but if you can't see the cards and no one can change the table's hand based on what they see, it doesn't matter. it's the same reason why you ALWAYS take the second door in "Let's Make a Deal. " Always, always, always. for those unfamiliar, captain douche would offer you a prize behind one of 3 doors. he'd let you choose one door, but before opening it, would open one of the other 2(always empty) and then ask if you want to change your mind.
you'd think its 50/50, but it isn't. the difference here is he knew which door to open since he knows where the prize is. there's no chance of him actually opening the prize door. the easiest way to show this is that if you always switch, the ONLY time you will lose is if you picked the right door the first time. and the odds of that happening are only 1/3. math = wonderful. now to see if raytheon'll pay for me to get a piece of paper allowing me to teach it on the side. 
