Lay away is pretty much a savings account without the interest accrual as I understand it. That being the case the sale transaction shouldn't occur until you've saved enough to buy it (and that would be when the warranty starts).
Whether it's a good idea? Financially I've never thought layaway makes much sense. The only people it benefits are those with impulse spending problems by keeping the money out of reach. You can always save your own money in an interest bearing account or investments until you have enough so at least you get something in the mean time. However, with the current interest rates on savings and even CD's the profit would be minimal.
Another option is to apply for a line of credit. You will end up paying more for carrying a balance on a normal credit card but if you can get one with 0% for x months and pay it off before x months is up then it costs you nothing and improves your credit rating.
And if you don't have good enough credit to get such a deal then I would recommend starting. Apply for any credit card no matter the interest rate and use it for all of your purchases, making sure to pay it off in full every month before you get charged interest. I wouldn't do this for the laptop though unless you can pay it off immediately; the interest rates offered to people without credit are terrible and you will pay a ton for carrying a balance. Then next time you apply for a line of credit you can get a better deal.
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station…
