BSA Software Audit

I am a new IT director(my predecessor was fired and I walked into this position cold, no communication between myself and the previous IT director) and my company recently received an Audit letter from the BSA. What is the best way to discover and document the hardware and software licenses on the network? There is a total lack of documentation for what software is installed on what workstation. I tried WinAudit, but that does not pull the information I need to prove compliance. Network Inventory Advisor works well but that is a paid program. Has anyone survived an Audit? I could use some help on a plan of action.