Hi Baris,
You may want to look at the Digi Connect ME Integration Kit rather than the NET+OS development kit. It is not as flexible, but it includes a few things that NET+OS does not include, such as RCI and Java Applets.
If you do look at the integration kit, the modules should end with -S instead of -C.
You can, of course, write this with NET+OS and the -C modules, but it may require a bit of extra work to add modbus (there are free samples of modbus code located at http://www.protocessor.com web site) and to add specific HTML pages.
Best regards,
John Leier
Digi International