Just a good summary of process identity and the various options for ASP.NET and IIS.

(doesn't speak too much about IIS6, which is where I need the help - can't find NetworkService account when trying to add to DCOMCNFG)

317012 - Process and request identity in ASP.NET

Also found these articles about IIS6, machine accounts, groups, etc.
IIS Insider

IIS 6 and built-in accounts