I want to download iWork or Pages from the Apple store. I click on the purchase for $9.99 button, then it turns green (download app). I click again, but then it says “incompatible with the iPad.” What’s the problem?
You need to update your iPad to iOS 5. Plug your iPad into your computer and first update your apps from iPad into iTunes, then update iTunes, then the iPad. It says it will take long, but it didn't really. You then will find all apps will work, as well as some updates that didn't.
My first guess would be that you didn't update your iPad to iOS 5 yet.
All iWork Apps (Pages, Keynote, Numbers) require the latest release which is iOS 5 at this time.