Keep people posted. It's not difficult to send out status email from time to time. Tell them things like, "We had a successful first round of testing on the servers," and "Reminder: Tonight we're testing the domain controller, IIS and SQL servers." Err on the side of too much communication. No one ever got in trouble for that.
Setting your Windows security assessment expectations
Step 1: Determine the business goals
Step 2: Get input and information from others
Step 3: Let everyone know that problems will likely occur
Step 4: Let your testing be known and keep people in the loop
Step 5: Report what happened
About the author: Kevin Beaver is an independent information security consultant, speaker and expert witness with Atlanta-based Principle Logic LLC. He has more than 19 years of experience in IT and specializes in performing information security assessments involving compliance and IT governance. Kevin has authored/co-authored six books on information security including Hacking For Dummies and Hacking Wireless Networks For Dummies (Wiley) as well as The Practical Guide to HIPAA Privacy and Security Compliance (Auerbach). He also created the Security On Wheels series of audiobooks. Kevin can be reached at email@example.com.