i am doing a project on how to select a stepper motor to drive a robot? i
can't find anything on the web....
i have found books for sale only.....

This is to both the poster and the researcher. Go to the library and
read trough the books that you found for sale. I am a hobby robotist
and found the internet utterly usless for information on the subject.

I couldn't find the answer to your question but I did find two
wonderfully extensive pages of robotics links, including several links
on the topic of stepping motors:

http://www.rdrop.com/~cary/html/robot_links.html
http://xedox.de/roboterlinks.html

I am not sure if I could answer your question, because it depends on what
application for which you are building a robot.  All that I can say with
my limited use of stepper motor is as follows:
i) Make sure you have enough power(torque/step) for the application.
ii) Depending on if you would like finer resolution, you could go with one
that has small degree/step.
iii) The other parameters to watch for are the continuos duty rating,
holding torque etc.
You might also have to spend some time investigating the suitable drive
electronics to match the motor power requirements.
There are two type of stepper motors available, uni-polar and bi-polar.
The bi-polars are outdated but should be availabe in higher ratings from
surplus stores.  It might also be difficult to get a drive circuit for the
same.  The uni-polars are more easier to get, but may not have very high
torque.  It should be fairly easy to drive them through a computers parallel
port without any additional drive circuitry(except for isolation and power
amplification).
You might find the following places useful:
http://www.qkits.com
http://www.ramseyelectronics.com
http://www.hvwtech.com
http://www.oricomtech.com
http://www.allelectronics.com
http://www.meci.com
http://www.allcorp.com