Recently a strong research effort has been spent on Vehicular Ad-Hoc Networks to evaluate, also by simulations, the effectiveness of protocol solutions. The difficulties lie not only in the definition of realistic simulation environments (including mobility, propagation effects and large number of nodes), but also in the precise comprehension of the results achieved. In fact the outputs hardly allow an extensive understanding of phenomena, due to several aspects such as mobility, position-dependent performances and transitory effects. A custom visualization tool, like the proposed VisMagna, can represent the right solution towards the understanding, debugging and comparison of protocols. VisMagna is here presented for the first time, adapted and applied to the comparison between IEEE 802.11p and MS-Aloha, a slotted solution based on the same physical layer of IEEE 802.11p.