I recommend the following resources to focus you on coding without
getting overwhelmed:

http://blog.charlescarroll.com/chazblog/?p=502
I choose these sites including the bite sized examples from Dave And
Al's site, and the complete CodeProject articles that are frequently
updated and focus on small to medium sized tasks rather than the
architecture centric "heavy" examples the Starter Kits and www.Asp.net
throw at you to drown you and overwhelm you. The book ASP.net
Unleashed is invaluable because they focus on a 1 page  at a time
approach needed by newbies yet "graduate" you to building whole sites
and they focus on the "whys" and the how and the whys really are the
stumbling blocks for most overwhelmed people.

What you used to do with Includes could be done with User Controls
(NOT server  controls) or in some cases Master Pages (making many pages
appear the same without includes) and they provide you a good sense
for how much cleaner things can be with encapsulation and flexibility
on the ASP.net side.
www.charlescarroll.com/chaz/site/4806/default.aspx - has some
User Control basic articles

The login control can be customized of course with themes. It is a
very mature feature. and tied with Forms Authentication can reduce
your workload quite a bit. All the Scott Mitchell articles on Form
Authentication are the next best thing to the Walther book if the
Quick Starts are too sketchy for you. Be sure and check out:
www.charlescarroll.com/chaz/site/4751/default.aspx
these articles really help you wrap your mind around the power and
ease of these authentication and profile features and why a little
more work  up front saves you a ton of work down the road.

MetaBuilders.com has some great FREE controls to simplify common tasks
and show you how such things should be done JUST DROP THE DLLS IN \BIN
directory and use them at first and wait until later to delve into the
source code till after you read the Walther ASP.net Unleashed chapters
on Server Control building.

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==
Tackle this stuff after you have got a good practical knowledge of the
above and asked us a few dozen questions on the group about it all as
you convert your includes to UCs and Master Pages, and have your first
page through a dozen simple pages perpared with the resources above
and help from this group.
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==

If you like User Controls (I luvvvvvvvv them) WebParts are UCs on
steroids and if you rewrite your UCs as WebParts your code is
SharePoint ready and you are way ahead of most "veterans" who ignored
the radical new paradigms WebParts allow see:
www.charlescarroll.com/chaz/site/4807/default.aspx

The SiteMap is one of the crudest features in ASP.net - great at the
basics but a LOT of work. I would tackle that last. LAST LAST LAST.
www.charlescarroll.com/chaz/site/4845/default.aspx will help
you find  some better articles when you get to that phase.