Windows XP's successor Vista has launched a little while ago. For EA a reason to put up a page about the compatibility of the Sims 2 with the new operating system. Since Vista is heavier the game will have some higher requirements and it might perform less well as on the same machine with Windows XP. There might also be some problems with Vista's compatibility with graphics cards. Some cards supported by the Sims 2 are not supported on Vista, which is mostly a drivers issue that the card manufacturers are working on. Besides that there are some issues with the Autorun requiring Administrator access, meaning you'll need to use the Game Explorer or the Start menu to launch the game. For Seasons it's explained that the start menu icons will only appear for the user installing the game (the administrator). New icons need to be added for every other (standard) user that needs to run the game. More details, including specific issues for specific graphics cards, can be found on the Vista Q&A Page on the official site. Thanks to SnootySims for the link.