Ron (Vridar),
This is getting more technical than I ever intended, but I'll try to keep it is as simple as I can.
Your question about a transformer that is 6 volts and a resistor of 280 ohms is certainly the right idea, except for the fact that the LED behaves peculiarly. LEDs tend to maintain a fixed voltage across them regardless of current flow. This one remains about 3.3 volts (shown on the package) across it all the time. You need to make a calculation based on the difference, something on the order of 8.7 volts across the resistor. I calculated it this way and when I measured the current, it wasn't quite what I expected. With electronics, reality rarely exactly matches the math on paper. It's just a starting point for design and testing.
Ultimately I measured the current with a meter while trying descending values, but starting above the range I had calculated. So as to not feed an LED too much current, it is always good to start with a higher resistance than you calculate and work down. Give me a day or so to post how to make this measurement with a meter.
More generally, for the purpose of understanding volts, ohms and amps, I would draw an analogy (for this instance only) to water flowing in a pipe:
Voltage is like water pressure. The pressure is separate and distinct from the water itself. The higher it is, the more flow there is.
Resistance (in ohms) is like the size restriction of the water pipe. The greater the restriction, the lower the flow.
Amperes (amps) are like the water itself flowing. One amp is a huge number (I won't give it) of electrons passing a given point in one second. Amps are always a result. You can't alter current flow directly. All you can do is alter voltage and resistance to produce the amount of current flow that you want.
On the transformer you propose, 50 mA would be fine. Only 25 mA will be drawn or used, no matter how high the mA capability of the transformer is.
Because I work with electronics, I'm advantaged by having most standard resistor values on hand to test with. But most people don't. Radio Shack has them in 5 packs. Maybe you could get a few well selected values to try. You can experiment with smaller resistors connected in series (end-to-end). You simply add all the values together. 280 ohms isn't a standard value, but I believe that 270 is. You could get some 47 ohm or 100 ohm resistors and make test combinations. You could work down from around 560 ohms to whatever produces the desired current. More tack soldering practice! When you know how many ohms you need, use one resistor that replaces all of them.
I'll get pictures of the meter setup ASAP. John