According to the Allegheny County, Pennsylvania police site, inspection expires on the last day of the month indicated by inspection sticker (i.e. 12-08 would be December 31, 2008). They also note that the fine for expired inspection sticker is up to $25.00 plus costs. We have read that the fine usually ends up being around $100. If you are without an inspection entirely we have read that the fine ends up being around $200.
Section 1301 of the Pennsylvania Vehicle Code discusses the PA requirement for registration and certificate of title. Here it states the need for registration (in subsection a) and the penalty for not having your vehicle registered in subsection d) which you can read here:
(a) Driving unregistered vehicle prohibited - No person shall drive or move and no owner or motor carrier shall knowingly permit to be driven or moved upon any highway any vehicle which is not registered in this Commonwealth unless the vehicle is exempt from registration.
(d) Penalty - Any person violating the provisions of subsection (a) is guilty of a summary offense and shall, upon conviction, be sentenced to pay a fine of $75 or double the registration fee, whichever is greater, except when the vehicle was previously registered in this Commonwealth within 60 days of the commission of the offense whereupon the fine shall be $25. In the case of a motor carrier vehicle other than a trailer, the fine shall be $50 if the motor carrier vehicle was previously registered in this Commonwealth within 60 days of the commission of the offense or, if the registration occurs outside the 60-day period, the fine shall be double the registration fee for the maximum weight at which the vehicle could have been registered in this Commonwealth.
So if you drive without an inspection sticker and registration you can be stopped by Pennsylvania law enforcement. If you were cited for driving without an inspection sticker and for not having registration on your vehicle in Pennsylvania then you should contact the court listed on the citation to find out about the fines that you will receive and if there will be any other penalties attached to these violations.