i was arrested feb 08 the state of pa withdrew charges on me what are the chances the feds pick the case up

There is no way to legitimately answer this question. You did not include what the charges were that were withdrawn. For example, if they withdrew a DUI charge, the feds to not prosecute DUI cases and there is no chance the feds will pick up the case. If the state withdrew drug charges, I would like to know why they withdrew those charges. For example, the PA Constitution protects the individual more than the US Constitution, so if a search violated the PA Constitution, but does not violate the US Constitution, AND it's a major case, then there is a good chance that you will be charged on the federal side.

As for the statute of limitations, again, there is not enough information posted to give a meaningful answer. When is the alleged offense date? That is the time when the statute of limitations begins to run. As for it being wise, it's always wise to stay out of trouble.

No one can even begin to assess whether the feds will pick up your case without knowing the particulars of what your case was, why charges were withdrawn, whether there exist analogous federal charges, whether you have a criminal history, and other factors which may indicate whether the federal government would have an interest in your case. If you would like to explore this further, it is wise for you to consult with an experienced federal criminal lawyer.

(Please note that this response does not constitute legal advice nor does it establish an attorney-client relationship.)