Computer simulations offer great possibilities for the investigation of such complex materials as polymers. We can polymerize chains, define and control any possible cross-linking reaction and generate in this way polymer networks of different but known structure. In this contribution we focus on the effect of different precursor structures on the density and formation of entanglements by the cross-linking process and we discuss their possible contribution to the modulus or swelling behavior of the networks. To test our results we simulate swelling and deformation experiments with networks of different structure and different density of entanglements. In addition we measure the mobility of different types of polymers and cross-links and compare the results within the same network or within networks of different structure. This test allows for a direct measurement of the constraints of network structure on the molecules and it allows for a comparative estimate of the contribution of different structural units to the properties of the whole network.