How can I extract dept or category data for OTB (open to buy) planning?

Go to your database server.
Run Manager, Utilities, Crystal Reports, DRS Sales Summary report, select Criteria tab, Date Closed, Between, enter a date range such as 1-1-2013 to 1-31-2013, Add, Generate, then print.
Repeat for each month required.

Next run Manager, Reports, Custom, Purchase Order Valuation, enter a date range, OK to run report, drag category to leftmost column, then click Collapse icon in toolbar to view totals by category. Or leave dept in first column for totals by dept.
Repeat for each month required.

Next run Manager, Reports, Items, Inventory Valuation*, enter a date range, OK to run report, drag category to leftmost column, then click Collapse icon in toolbar to view totals by category. Or leave dept in first column for totals by dept.
Repeat for each month required.

That is all the data you need for OTB planning (inventory levels, purchases, and sales).

*If you do not find Inventory Valuation listed, it means you are not running RMS 2.0 Feature Pack 1 or higher (example, 2.0.0155). See separate KB article on how to estimate inventory levels for historical periods:
How can I create a historical Inventory Value Report for a prior date? - Digital Retail Solutions (kayako.com)

IMPORTANT: This article is also the recommended method to obtain historical valuation if the Valuation report by date range does not generate expected numbers (known issue).