I am trying to setup quotas to PE collaborative forecast. When I go to the customize - forecast - setup section, I do not see the "Show Quotas" checkbox as described in the documentation (page 14) http://na9.salesforce.com/help/pdfs/en/forecasts.pdf
Setting up quotas requires API access, so Professional Edition doesn't seem to have quotas. You wouldn't be able to set up the feature anyway.
(Yes, there is the AppExchange package, but that seems to be only for Enterprise Edition and above. https://appexchange.salesforce.com/listingDetail?listingId=a0N3000000B41EqEAJ)
If you contact support to discuss - there is a chance they can switch your forecast settings from a Collaborative Forecast to Customizable Forecast (which includes Quotas as a feature for Professional Edition).
I am currently working with support to facilitate this in my org. As a heads up, it will require them to purge Collaborative Forecasts completely from your system and reinstall a new package: the Customizable Forecast. If you have data currently loaded into your forecast, you will need to back it up before the migration and reformat & load it after the new package is installed. Hope this helps... I can repost after the migration is complete with any additional findings.
The solution is to upload the quota data via the data loader. You have an option to upgrade to EE. Alternatively you may be able to use a third party data loader, e.g., Jitterbit Data Loader to upload your data. Salesforce stores the quota information on the user record when collaborative forecasting is enabled for the org, previously it used a separate Quota object related to the User object to store the information. I would therefore suggest take a listing of the users in a CSV and add the quota data in a separate column and then to upload this via the data loader (see options above). This way you will be able to see the user quota in the forecasting tab (and not on the user record).