What does your network look like.
1. How many windows workstations?
2. How many windows servers?
3. How many unix/linux workstations?
4. How many unix/linux servers?
5. How many and what brand of routers, switches, hubs?
6. Do you have recent backups of all systems?
7. Were all computers affected or select few?
8. Can provide a graphical layout of the network?
If you can answer some or most of these questions ill be able to tell you how to start the cleanup process.