Sounds like you will have a good system Bojan. That sensor that you gave me the specs on is definitely a good option to use with the encoder wheel that I intend to use. to use it without mechanical parts I could print out a large encoder wheel with the required resolution of 4000 tics. If the sensors are easy to source they would be a gold mine.
Ok what I have come up with so far is:
I have pulled a spindle out of an old CD drive - it will be used for the axle to drive my encoder wheel.
I have found to necessary software to make an encoder wheel that everyone can download for free:
encoderwheelv1.3.ps - Encoder Wheel Generator by NickAmes:
http://www.thingiverse.com/thing:1527
The instructions are on the web site.
GSView and Ghostscript - Postscript file viewer. you can find a version by just Googleing it. You need these programs to view the wheel encoder and print it if you are not a computer nerd like me.
A few old CDs' - Everyone has them!
As far as the optical transmitter and receiver goes I think the cheapest solution is buy savaging an old mouse. That is covered by other posts so I won't mention the process here. the trick with the wheel is that you need to print your wheel on an over head transparency.
The turn ratio will be around 4:1 which is a reasonable ratio as the chance of slippage will be reduced significantly. To make the main planetary friction wheel I was thinking of gluing about 6~8 old CDs' together. using the old CD spindle and CD planetary friction wheel will give me around 5,400 ticks which will do the job nicely.
I will follow up with pictures and more details as the project progresses.