Lee159,
i just want to clear something up. There are actually many types of seizures a person can have. If you do choose to categorize them into two groups, you forgot one. The two types you named (absence/petit mal and tonic clonic/grand mal) are both generalized seizures. There are also partial seizures (the most common type in adults by the way) which can be categorized further into simple partial and complex partial. Partial seizures stem from only part of the brain, so they can present themselves in countless ways--just read the posts on this site!
It is therefore possible that involuntary leg shaking could be a seizure, although it's probably not the case (or at least not worth worrying about) in this situation. Jennifer, you should ask a doctor if you're concerned though.
Jen