What is it?
Office Startup Assistant - Osa.exe
What does it do?
The Office Startup Assistant (Osa.exe or OSA) is a program that improves the performance of Office XP programs. Office Setup places a shortcut to the Osa.exe file in the Windows Startup folder; the file is named "Microsoft Office".
Microsoft's information page.
You'll want to keep an eye on this google search for any known viruses. The normal location of this file is C:PROGRAM FILESMSOFFICEOFFICEOSA.EXE