Douglas Robar have created some excellent and detailed "umbraco books" on how to install umbraco 3 on Vista and umbraco 2.1 on XP. Douglass is by the way the creator of both ImageGen and XSLT Search, two fantastic add-ons to umbraco and he's even available for hire!
If you need to install v3 on XP, you can combine information from the two books. Kasper Ulvedal is working on a book on installing v3 on XP, but that's work-in-progress and not completed yet (we need a way to mark a book "in-progress" to ensure that people don't get confused about empty or semi-empty books).
If you need to upgrade v2.x or a pre-release version of v3 this is the process:
- BACKUP files + db(seriosuly)
- If you've installed any packages that has own create dialogs (like the RSS module), make sure to keep a copy of /umbraco/config/ui.xml nearby
- Unzip the downloaded release file v3xxx.zip
- Copy /bin, /config, /install, /python, /scripts /umbraco and /umbraco_client from the zip into your v2/rc1 installation (yes, to overwrite)
- Update web.config and the new /config/*.config with the settings from your old /config/*.xml files if you've changed those (Make sure that you base the web.config on the new one and just copy your changes. The new one includes lots of important references!)
- Copy the ui.xml back in place if you had that changed
- Go to your website and the upgrade process should begin automatically