Updates to a Exisitng Program

Several years ago we had a program built to automate our purchasing process. This program connects to our QuickBooks software and calculates which items we need to order, how many and from where. The software then creates purchase orders in QuickBooks for us to process. We need several updates to this software: 1 - bug fix. Sometimes the software skips over products. We need to find out why these are being skipped and fix it. 2 - bug fix. The software does not always work correctly when faced with 0 or negative numbers. 3 - enhancement. Currently the software looks at how many of an item we have in stock and the reorder point (defined in QuickBooks) to determine how many to order. We need to change this to look at the current stock, the reorder point, and how many of the item were sold during a specified time period (based on user input). 4 - enhancement. Currently the software displays a list of all purchase orders that need to be placed and we can export all purchase orders at once. We need a way to export only certain purchase orders. 5 - enhancement/bug fix - currently we can see all items that are on a purchase order, add or remove items or change quantities within the software. When exporting the purchase order, however, all changes are lost. This needs to be fixed. The software is written in VB.NET and was originally targeted to QuickBooks 2005. We have since upgraded to QuickBooks Pro 2008. So far this has not been a problem, we need to ensure that the software continues to work with 2008.