Needing some FHA advice.....

I'm a potential first time home buyer who has a decent salary but not alot in the bank.  I realize that FHA limits this necessity but I am still weary on how much my down payment will have to be and what my closing costs will be.  I realize some of this can be negotiated in the sale itself, however, the worst case scenario is that it the seller doesnt agree to pay closing costs and I have to come up with them.  I am looking at the 150k range for a house and wanted to know (a ballpark figure obviously) what the closing costs associated with a sale like this might be and also how much I would have to put down.  I realize its generally 3% but I am confused on the transfer of money between the buyer and seller.  I have friends that say they only had 5k to contribute to their sale and were able to buy a 150k house without the seller paying closing costs.  I'm just trying to get educated here!  Need some guidance so I know how much to have in my pocket going into this thing.  My goal is to make this all happen this summer.  THANKS!!!!!!!