What exactly can one do to protect themselves both proactivly (in security and legal sense) and what to do if that administrator attempts to frame her for some sort of misconduct.
Make an escape plan. Update your resume, work your contacts, and find what openings there are at other companies. It may seem cowardily, but retreat is an attempt to pretect something of value from further damage.
Find your friends. Who you know that works in physical proximity and could be used as a witness to your activities. Who you know higher up in your department or division that has power or political capital within your company.
Find the admin's other victims. If he is malicious, chances are he has annoyed others. Finding enough people who have been victims of his maliciousness may convince an otherwise incredulous higher-up.
Comply entirely with company policy even if it is stupid. If you find you are unable to comply because it compromises your ability to work, bring the issue to the appropriate person urgently. Be polite but firm until you have piece of paper with an exemption or rule change with the person's signature on it. Do not foolishly assume that the number or severity of policy infractions matter. A single infraction on a rule that is never enforced may be enough for dismissal.
Do Not Bring Your Own Laptop! Especially if this is unusal behavior for you or other people at the company. Do not bring in anything that could be used to record, photograph, copy, store, etc. This means no cell phones, no iPods, no MP3 players, no portable game devies, no USB thumb drives, no SD cards, etc. If the admin is capable of planting evidence, he may be able to persuade a company represantative that you are planning to steal company data. Even if you have no company data on your devices, the threat of attempted theft may make ordinary devices seem suspicious. However having no devices capable of copying or recording this data, nullifies this type of allegation.
Unless it is necessary for your work, do not take work home, do not take any papers, equipment, or supplies belonging to the company out of the building.
Whenever practical work with someone else, preferabily a friend. The only way to counteract technical evidence is with human evidence. Keep track of the time and make whoever you are with aware of it as well. Any technical evidence against your will be timestamped, you need a human witness to be able to provide counterevidence of the same time period. Not necessarily the exact time, but something along the like of "From 10:00 to 10:15 Ann was editing a document, not surfing the web."
Make friends in high places. If your do not know, find out exactly who has the ability to fire/dismiss/let-go of employees. Try to present yourself positively to as many of those people as you can.