Well actually it is, because the concept is the same only some bottom line things have changed (e.g. in the currect website model of dnn4 modules are a part of the DotNetNuke project - website)

for a good explanation on how to build the modules initialy in dnn4 read Shaun's posts on asp.net forums

http://forums.asp.net/thread/1114393.aspx

all the rest applies (module structure by layers, module services, etc...)

hope this helps, good luck!