I have two customers that both order item A. One customer requires just in time deliveries, and the other does not. For the just in time customer, we would like to build item A to a forecast, but for the other customer, we want to build item A to sales order demand only.

Is it possible to set this up in Baan without making A into two different items? Lets say I forecast 100 units for the next month for item A– 50 for the just in time customer, and 50 for the other customer. I would like to enter this forecast into baan for 100 units, and to have baan drive planned production orders for the 50 units forecasted for the just in time customer. The remaining demand & production build will depend on how sales orders come in from the non just in time customer.

Wile this is a simple example, we have hundreds of customers ordering thousands of SKUs, so creating a new SKU for each one of these situations is not feasible.

Use PCS to manufacture the MTO item (same item, only has projectorder attached to it.)
Then the standard item is linked to the project item. If they are the same, keep it linked. If the projectitem has a (small)change then unlink the standard item and modify the routing and/or BOM for the project item.

Forecast is all what you think to do next period (and is always wrong calculated :( )
Actual orders will consume the forcast. If you do not unlink the standard item from the projectitem, forecast can be done on the standard item for both.

Gold solution - however I do not want to have to implement projects.....

How about entering the "forecast" as a sales quote with a higher enough success percentage to drive planning?

Interesteing idea - can you explain a bit more to how this might work - I have not used sales quotes much

Your sales orders to your MTO customer will drive demand for "actual" sales. By entering a quote with a high success percentage for your MTS you can drive demand for an additional quantity equal to you forecast. I am on 4c3 so am not sure how the planning works in 5 but in 4c3 you can set whether quotes should be considered by planning and if so what percentage threshold has to be attained in order to drive demand. Have never done so I am really just thinking out loud. Sometimes the crazy ideas end up solving the problem so figured I would throw it out there.

I like the concept. ill try it out.

The only downside would be that there are about 100 items that I would have to key in individually into the quote each month - but it may be my only choice

You might also look at using Special Demand for the Item which acts like a forecast for the item.