First, there are two SiL lectures, about the IP protocol family (part 1 will be on 31/5/2004, and part 2 will be on 28/6/2004). These are actually re-runs of lectures 16 and 18 (see the old lecture slides on the web site), and will cover the working of the IP protocol (which makes the internet tick) and its family (TCP, UDP, routing protocols, a little about higher-level protocols if we have enough time).
Then, there will be a new lecture about "doing things" at the IP protocol level - sniffing, creating IP packets, hijacking IP traffic (and NOT for criminal purposes, mind you). This lecture will be given on 19/7/2004, and is intended for both SiL and non-SiL audiance (i.e. in order to be able to understand this lecture, one needs to know about the IP protocol family in the level that will be covered in the previous 2 "IP protocol family" lectures). This lecture will also require knowledge of programming in C, since most tools that will be mentioned are to be used from within a C program. (The SiL lectures do not deal with programming at all, and do not require any background in programming).
Slides available here