The Shulchan Aruch (based on the Talmudic discussion in Tractate Yevamos) explains that gerim (converts) are presented with samples of some of the heavier and lighter laws of the Torah prior to the conversion (and that a formal acceptance of Judaism in the presence of a Beis Din must occur in order for the conversion to be valid). Why are samples of Torah strictures taught to a ger? Must he not first know the entire Torah?
I think that the answer is that the ger's learning experience is designed to make him conscious of his prospective commitment. In order for his conversion to be legitimate, he needs to be aware of the new lifestyle he will lead. Thus, a sampling of heavy and light Torah laws are studied in preparation. Once the non-Jew is a Jewish, he can then learn the rest.
The Jewish People left Egypt as freed slaves. Slaves have little or no concept of overall responsibility for property, monetary transactions and personal damages, as they are not in real control of money and property. As such, it was appropriate that the gerus of Bnei Yisroel focus on the civil laws which comprise most of the parshah, as this area of Torah would be the starkest contrast to life as they knew it in Mitzrayim, and it was thus requisite for a conscious conversion, so that they become aware of the lifestyle they would enter upon formal conversion. In other words, presentation of the Aseres Ha-Dibros fulfilled the general rule that a ger must be taught a sampling of the basics a Judaism. However, additional instruction was necessary in this case, as the Jews had to become conscious of the obligations of Torah in their role as freed slaves, and the civil laws of Mishpatim serve this end. It is thus understood why the formal acceptance of Torah occurred at the end of the parshah, accompanied by sacrifice and the other elements of conversion (see Rashi). The gerus which was initiated in Parshas Yisro was continued through Mishpatim, such that both parshiyos form one continuum.