Okay, let's assume that msiexec.exe
invokes a helper and that helper invokes whatever is causing the HTTP traffic. Right after the first helper spawns the child it kills itself. This process is too short-lived to normally see the relationships here.
Enter the "Process Tree" feature of Process Monitor. Keep Process Monitor running without any filters on process events. After you are done you can then press Ctrl+T to see the Process Tree (see below).
The grayed icons tell you the process is not active anymore. Furthermore the last column is the end time of the process. But best of all you can see which process created which other process from this, even for very very short-lived processes.
Mark Russinovich, author of Process Monitor and its predecessors, demonstrated this at TechEd about a month ago.
Although this may not answer the question entirely, it should get you going in the right direction. After all Process Monitor also includes network activity filtering (albeit crude, compared to Network Monitor and Wireshark :)).
btw: the green bar in the above screenshot is the "timeline" where you can see the runtime of the process in relation to other processes. Very nifty.