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!