The only way that I know of to make a new background with out altering all other windows backgrounds is to define a new border. It seems that SoE bound the background to the border instead of making it a selectable thing. In this case the new background is put into a copy of the WTD_Rounded border.
Just copy this and put it into your item inspect window, change the "spiffynewbackground.tga" files to the name of your background picture.
If anyone knows an easier way please post it, as I have tryed just about every thing to no aval.
<TextureInfo item = "spiffynewbackground.tga">
<Size>
<CX>256</CX>
<CY>256</CY>
</Size>
</TextureInfo>
<WindowDrawTemplate item = "WDT_Iteminspect">
<Background>spiffynewbackground.tga</Background>
<VSBTemplate>
<UpButton>
<Normal>A_VSBUpNormal</Normal>
<Pressed>A_VSBUpPressed</Pressed>
<Flyby>A_VSBUpFlyby</Flyby>
<Disabled>A_VSBUpDisabled</Disabled>
<PressedFlyby>A_VSBUpPressedFlyby</PressedFlyby>
</UpButton>
<DownButton>
<Normal>A_VSBDownNormal</Normal>
<Pressed>A_VSBDownPressed</Pressed>
<Flyby>A_VSBDownFlyby</Flyby>
<Disabled>A_VSBDownDisabled</Disabled>
<PressedFlyby>A_VSBDownPressedFlyby</PressedFlyby>
</DownButton>
<Thumb>
<Top>A_VSBThumbTop</Top>
<Bottom>A_VSBThumbBottom</Bottom>
<Middle>A_VSBThumbMiddle</Middle>
<OverlapLeft>0</OverlapLeft>
<OverlapTop>0</OverlapTop>
<OverlapRight>0</OverlapRight>
<OverlapBottom>0</OverlapBottom>
</Thumb>
<MiddleTextureInfo>scrollbar_gutter.tga</MiddleTextureInfo>
<MiddleTint>
<Alpha>255</Alpha>
<R>128</R>
<G>128</G>
<B>128</B>
</MiddleTint>
</VSBTemplate>
<HSBTemplate>
<UpButton>
<Normal>A_HSBLeftNormal</Normal>
<Pressed>A_HSBLeftPressed</Pressed>
<Flyby>A_HSBLeftFlyby</Flyby>
<Disabled>A_HSBLeftDisabled</Disabled>
<PressedFlyby>A_HSBLeftPressedFlyby</PressedFlyby>
</UpButton>
<DownButton>
<Normal>A_HSBRightNormal</Normal>
<Pressed>A_HSBRightPressed</Pressed>
<Flyby>A_HSBRightFlyby</Flyby>
<Disabled>A_HSBRightDisabled</Disabled>
<PressedFlyby>A_HSBRightPressedFlyby</PressedFlyby>
</DownButton>
<Thumb>
<Right>A_HSBThumbRight</Right>
<Left>A_HSBThumbLeft</Left>
<Middle>A_HSBThumbMiddle</Middle>
<OverlapLeft>0</OverlapLeft>
<OverlapTop>0</OverlapTop>
<OverlapRight>0</OverlapRight>
<OverlapBottom>0</OverlapBottom>
</Thumb>
<MiddleTextureInfo>scrollbar_gutter.tga</MiddleTextureInfo>
<MiddleTint>
<Alpha>255</Alpha>
<R>128</R>
<G>128</G>
<B>128</B>
</MiddleTint>
</HSBTemplate>
<CloseBox>
<Normal>A_CloseBtnNormal</Normal>
<Pressed>A_CloseBtnPressed</Pressed>
<Flyby>A_CloseBtnFlyby</Flyby>
<Disabled>A_CloseBtnDisabled</Disabled>
<PressedFlyby>A_CloseBtnPressedFlyby</PressedFlyby>
</CloseBox>
<MinimizeBox>
<Normal>A_MinimizeBtnNormal</Normal>
<Pressed>A_MinimizeBtnPressed</Pressed>
<Flyby>A_MinimizeBtnFlyby</Flyby>
<Disabled>A_MinimizeBtnDisabled</Disabled>
<PressedFlyby>A_MinimizeBtnPressedFlyby</PressedFlyby>
</MinimizeBox>
<TileBox>
<Normal>A_TileBtnNormal</Normal>
<Pressed>A_TileBtnPressed</Pressed>
<Flyby>A_TileBtnFlyby</Flyby>
<Disabled>A_TileBtnDisabled</Disabled>
<PressedFlyby>A_TileBtnPressedFlyby</PressedFlyby>
</TileBox>
<Border>
<TopLeft>A_RoundedFrameWithTitleTopLeft</TopLeft>
<Top>A_RoundedFrameWithTitleTop</Top>
<TopRight>A_RoundedFrameWithTitleTopRight</TopRight>
<RightTop>A_RoundedFrameWithTitleRightTop</RightTop>
<Right>A_RoundedFrameRight</Right>
<RightBottom>A_RoundedFrameRightBottom</RightBottom>
<BottomRight>A_RoundedFrameBottomRight</BottomRight>
<Bottom>A_RoundedFrameBottom</Bottom>
<BottomLeft>A_RoundedFrameBottomLeft</BottomLeft>
<LeftTop>A_RoundedFrameWithTitleLeftTop</LeftTop>
<Left>A_RoundedFrameLeft</Left>
<LeftBottom>A_RoundedFrameLeftBottom</LeftBottom>
<OverlapLeft>0</OverlapLeft>
<OverlapTop>0</OverlapTop>
<OverlapRight>0</OverlapRight>
<OverlapBottom>0</OverlapBottom>
</Border>
<Titlebar>
<Right>A_RoundedFrameTitleRight</Right>
<Left>A_RoundedFrameTitleLeft</Left>
<Middle>A_RoundedFrameTitleMiddle</Middle>
<OverlapLeft>0</OverlapLeft>
<OverlapTop>0</OverlapTop>
<OverlapRight>0</OverlapRight>
<OverlapBottom>0</OverlapBottom>
</Titlebar>
</WindowDrawTemplate>