First things first - so you want to install and use the latest and greatest development tools for the latest and greatest mobile platform? Easy. Just go here, and follow the instructions. If you don't have a Windows Mobile 5.0 device (and, well, that's not likely just yet), don't worry as the included emulators are superb.
As for the documentation for Windows Mobile 5.0, you'll find it right here on MSDN. We're updating it regularly, so keep checking back for a growing number of topics and examples. And of course, if you want something in particular included, tell us! You can either email me, or add a comment, or send email to the documentation feedback team (email@example.com) and we'll get it and add it to the list of features we're working on.
But I know you - you're a developer, and you want sample code, right? Well, once you install the Windows Mobile 5.0 SDKs, you'll find that you have also installed a bunch of 80 or so samples. You'll find them in:
\Program Files\Windows CE Tools\wce500\windows mobile 5.0 Pocket PC SDK\Samples
\Program Files\Windows CE Tools\wce500\windows mobile 5.0 SmartphoneSDK\Samples
The examples just plain rock, so enjoy!
If you are a new to Visual Studio and Mobile development, I've some great news - we have some excellent videos you can watch, and they'll be online for your viewing pleasure in the next week or so. Watch this space.