C# Definition:

public enum WallPaperStyle : int
{
     WPSTYLE_CENTER = 0,
     WPSTYLE_TILE = 1,
     WPSTYLE_STRETCH = 2,
     WPSTYLE_MAX = 3
}

VB Definition:

Public Enum WallPaperStyle
    WPSTYLE_CENTER = 0
    WPSTYLE_MAX = 3
    WPSTYLE_STRETCH = 2
    WPSTYLE_TILE = 1
End Enum

Notes:

See IActiveDesktop::GetWallpaperOptions and IActiveDesktop::SetWallpaperOptions