two questions:
1-i am about to develop a commercial application and encode it before distribution.if i use ZF, will i be violating the license if i enocde my files ?
2- for users to run my application, do they have to find a host with special requirements or setup?

thx in advance

From the lisence:
Edit: to clarify, the above means that it's ok for you to encode your source as long as the ZF lisence is provided with the distribution.

To answer your second question, yes the host would have to run the matching parser to your encoding software. Meaning that if you use FooEncoder to encode your source you would have to use FooDecoder on the host.

Check with your host, many install ionCube and/or Zend Optimizer by default. A quick phpinfo() should let you know which one, if any, is installed.

i am worried about the ZF itself.for users to run my application, do they have to find a host with special requirements or setup (regarding the ZF) ?

PHP 5.2 is all that is needed afaik.

Take a look at the requirements, take special note of PHP Extensions (page 2)

It's all about how you design your application.

well...those extensions should be available at the web host(of course related to the used ZF modules) for my customers to be able to run the application am i correct !!

have them run a phpinfo() script, then anaylze the results... then you can match them to what you're using in your project.