I am assuming you looking a MR16 spot lights which were 12 volt.
1) In theroy a transformer should run LED's in the same way as it did quartz lamps, however some LED's will only work with DC so depends on LED.
2) An electronic transformer is often not suitable for use will LED's often there is a minimum output.
3) Be very careful buying a driver, in theroy a driver controls current and a power supply controls voltage but it seems lighting manufacturers mix and match the names so you will likely need one which states 12 volt.
Your not the first and likely will not be the last to get caught up with lighting manufactures names. The toroidal transformer is as the name suggests a simple transformer but the electronic transformer is a switched mode power supply which often have minimum output and can produce spikes which will not harm tungsten lamps but will harm LED.
An LED needs a consent current supply often around 320 mA and we used a driver for this. But a LED package often has the driver built into the package so the driver built into the package often needs a consent voltage supply. For some reason which I have never worked out some manufacturers call the power supply designed for a LED a driver even when it's not. So forget the name buy by description if LED says 12 volt look for 12 volt supply and if it says 320 mA look for a 320 mA driver.
I fitted 4 x 0.58W spot lights in my bathroom and they failed after 6 months I will guess they want a smooth DC supply and my toroidal transformer gives a AC supply so likely the peak voltage it too high. I am sure if I bought better quality they would work on 16 volt peak but few bulbs actually state the voltage range. This firm
http://bedazzled.uk.com/12v_LED_Bulb_Replacement.htm is the only one I have found which actually states the range of voltage.
