Be sure to install these updates before installing Windows 7, to ensure full compatibility with the Apple hardware.
The updates will likely need to be downloaded and installed manually, since they may not show up in Apple's Software Update service.
An additional step for people who are upgrading is to download and use Apple's "Boot Camp Utility for Windows 7 Upgrade," which prevents the Mac partition from being accessed during the Windows upgrade process and causing an error code "0x80070005" from occurring, as described in this Apple knowledgebase document: Keeping your current installation?
If you are keeping your current installation of Windows, you do not need to install any updates from Apple to keep your current installation running as it is.
Windows 7 can only be installed as an upgrade from Windows Vista, and not Windows XP, 2000, or Server.
Additionally, an upgrade can only be done for a version of Windows 7 that is the same "bitness" as the current operating system.