newbie000,
It sounds like you have Powerpoint installed (like how you mentioned) on your server.
It also sounds like you are publishing out individual applications (instead of the entire desktop) which means you have to publish each individual application.
I would create a global group that will have "Office" access and give that group rights to the published application.
Here are the steps:
1. Create your global group.
2. Add users to global group.
3. Create publish applications (ie..word, excel, powerpoint, outlook..etc..etc)
4. Assign global group to published applications.
This way when they launch web interface, and if they have access to the app, they will see all of those icons.
You also mentioned that they can still open PPT files. This is because the app is already there on the server and they simply can not see the icon. By publishing out the icon they will be able to see it within web interface.
Hope that kind of helps.