Tiene problemas para convertir este NSString a NSDate [duplicado]

Posible duplicado:
¿Existe una forma sencilla de convertir una marca de tiempo ISO8601 en un NSDate formateado?

I can't convert this NSString to an NSDate: 2010-03-06T10:06:00-05:00

To be honest, I can not decipher the Unicode docs, where they talk about generic wall time , standard/daylight time, offsets from GMT as a fallback, etc.

To show that I have made a decent effort, here is what I have as the dateformatter: yyyy-MM-dd'T'HH:mm:ssZZ:ZZ"

If I strip out the timezone such that the date becomes 2010-03-06T10:06:00 then I know what to do. But how many letter "Z"s do I need, and are they upper case? Should I be removing the colon from the -05:00 ? The timezone has been my achilles heel with these conversions.

¿Podría alguien ayudarme?

¡Gracias!