Question: The title is quite self descriptive. I ask this question because I found contradicting information in the atmel web page. I need two external interrupts to control one rotary encoder. One interrupt control pulses from one pin (both rising and falling) and the other iterrupt the same for the other pin. So if I has only 1 it doesn't work for me.

* Visiting the product page at atmel I read that it has 6 Ext. Interrupts: <http://www.atmel.com/devices/attiny85.aspx>
* The datasheet I only see *int0* references (page 47) , and I don't quite understand the datasheet
<http://www.atmel.com/Images/Atmel-2586-AVR-8-bit-Microcontroller-ATtiny25-ATtiny45-ATtiny85_Datasheet.pdf>

Answer: 
There's INT0, and then there's PCINT[0:5]. INT0 gets its own interrupt routine, and the PCINT has one routine for all the pins configured to be used by the interrupt. That means that one of the first thing the interrupt routine needs to do is figure out which pin(s) actually changed to trigger the interrupt. Should actually be more convenient to use this way for your encoder, as you really want any encoder change to trigger the same interrupt routine.

I have no idea if all this is accessibile through the arduino platform, or if you need to program the controller yourself (as I'm not an Arduino user).
You can do this with a single interrupt if necessary by ORing the two pins into the one interrupt ("something changed"). You'll still need two digital inputs to read the encoder pins, and the ISR (or an exec-level helper routine) will have to take on the responsibility of figuring out which encoder pin(s) changed, but it's doable.