Whistler

Whistler is the codename of Windows XP.

Build 2410 and earlier
Until build 2410, Whistler did not feature any new wallpapers nor did it have a default wallpaper set. All of its wallpapers were reused from Windows 2000, due to it being fairly early in development. However, Build 2410 introduced a new default wallpaper titled Watercolor; every build of Windows in general has a default wallpaper from this point onwards.

Builds 2419 to 2463
While build 2410 introduced the Watercolor wallpaper, build 2419 introduced a small selection of the wallpapers that would feature in the final release of XP, while removing all of 2000's save for its branding wallpaper. Build 2428 changed the default wallpaper to Red moon desert, which would remain until build 2465; it was allegedly replaced due to testers comparing Red moon desert's appearance to buttocks.

The installation of Lab06 build 2415 shown at CES 2001 shows Bliss set as the wallpaper. As this build has not been leaked, it is unknown whether it was the default wallpaper in this build or not. If so, it could imply that Microsoft's design team were still trying to choose between Bliss and Red moon desert, or that the latter was just a placeholder, despite Raymond Chen's claims that testers were not happy with it.

Build 2465 onwards
Build 2465 introduced all of the wallpapers that would appear in the final release of XP. Bliss became the new default wallpaper. It also introduced a branding wallpaper, featuring a blue-white radial gradient background with the XP logo in the center. Unlike the rest it is at 1024x768 as opposed to 800x600. Starting with build 2485, the branding wallpaper was replaced with one featuring a CGI Windows logo. Between this build and 2532, it was set as the default wallpaper; however, builds 2535 onwards revert it back to Bliss.

A similar wallpaper is featured in a screenshot of build 2446 by Paul Thurrott. This one features a smaller logo with a transparent skewed “xp” in the center behind the logo, while the radial gradient is in the center left and the background is overall darker compared to the wallpaper introduced in build 2465. However, this wallpaper is not known to actually appear in any build, making it most likely that it was a promotional wallpaper Microsoft provided Thurrott themselves, privately. The wallpaper has not been made available online.

Sample Pictures
5 sample pictures at 480x336 were added in build 2474. With the exception of Winter forest (renamed to Winter), none of these were included in builds 2486 onwards, where sample pictures are at 800x600 instead.

User Account Pictures
Build 2419 introduced a small selection of user account pictures, compared to the final release. At this point, none of them are licensed from PhotoDisc; ones with known origins are licensed from Corbis, making it likely the unknown ones came from there too.