Sheez... a "medium sized" network? Mapping drives, changing permissions, etc. on 50+ computers would keep you busy for a week.
1. Create a logon script in active directory, mapping your network drive to each computer whenever a user logs on. As soon as your users log on, the drive automatically maps to each computer.
2. Edit group policy to hide the C drive from users http://support.microsoft.com/kb/231289 tells you exactly how to do this.
1. Start the Microsoft Management Console. On the Console menu, click Add/Remove Snap-in.
2. Add the Group Policy snap-in for the default domain policy. To do this, click Browse when you are prompted to select a Group Policy Object (GPO). The default GPO is Local Computer. You can also add GPOs for other domain partitions (specifically, Organizational Units).
3. Open the following sections: User Configuration, Administrative Templates, Windows Components, and Windows Explorer.
4. Click Hide these specified drives in My Computer.
5. Click to select the Hide these specified drives in My Computer check box.
6. Click the appropriate option in the drop-down box.
I would also edit the GPO to deny users local administrative rights on their machines.
You'd be done in less than 5 minutes. 30 if you're totally inexperienced.