Sometimes Eclipse does not register new plugins, so you need to clean out its cache. To do this run, Eclipse with the -clean command line option, like this
<eclipse-filepath.exe> -clean
If that does not work, then make sure that the OmniMark plugin was installed in your eclipse plugin directory. On the Stilo CTO's laptop this path is: C:\apps\Eclipse\3_1\eclipse\plugins. In this directory, you should see the following OmniMark directories:
If you do not see them, then you there was a problem with your install and you need to reinstall. If this condition persists then please contact Stilo support, see http://www.stilo.com/services/support.html for details.