OK, noob:
Having already setup Visual Studio, now download and install the ArcGIS SDK for .NET, get all of your service packs on, then start learning about "Add-ins", new at 10.0.
And beware, even though ESRI says there is "a lot" of documentation about Add-ins available, I am finding it EXTREMELY TRICKY to create an add-in that can open a standard Windows Form properly. Actually, I can get it to open a form, but the form is not "owned" by the application window, so it floats independently and can get hidden behind the application window or other windows if I'm not careful. I have found a grand total of ZERO help or discussion of this topic so far.
Otherwise, the Add-in mechanism is very cool, and once I figure out my little form ownership issue, I think I'm going to love it.
While it is true that you can get the VBA license from ESRI for version 10.0 only, it is a pain in the rear to install because it requires a separate license key. Plus, if you used to keep any VBA code in the User Template code module, you will be surprised to learn that ESRI has eliminated the user template (MXT file) at version 10.0, so now you must save your code in the MXD Document module. You can actually save code in the Normal Template module (yes, there's still a Normal template, but no user templates) but then you cannot call such code from a toolbar button or tool.
Welcome to ESRI's new world order.