в чем проблема подскажете???

C:\Denwer\home\testhost.ru> php composer.phar install
Failed loading \usr\local\php5\ext\php_xdebug-2.2.0-5.3-vc9.dll
Loading composer repositories with package information
Installing dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Problem 1
- zendframework/zendframework 2.3.1 requires php >=5.3.23 -> no matching pac
kage found.
- zendframework/zendframework 2.3.0 requires php >=5.3.23 -> no matching pac
kage found.
- Installation request for zendframework/zendframework 2.3.* -> satisfiable
by zendframework/zendframework[2.3.0, 2.3.1].

Potential causes:
- A typo in the package name
- The package is not available in a stable-enough version according to your min
imum-stability setting
see <https://groups.google.com/d/topic/composer-dev/_g3ASeIFlrc/discussion> f
or more details.

Read <http://getcomposer.org/doc/articles/troubleshooting.md> for further common
problems.

C:\Denwer\home\testhost.ru>

версия PHP какая?

Как сказано на сайте упомянутого денвера, там PHP 5.3.13
А zf 2.3.* требует не ниже 5.3.23. Соответственно, проблема очевидна: обновляйте PHP.