i know this can be found easily on google but i just modified it for dx9 and also made it easier to use(1 param req only)

Code:
void DrawRainbowXHair(LPDIRECT3DDEVICE9 Device_Interface)
{
	 D3DVIEWPORT9 gViewPort;
	 Device_Interface->GetViewport(&gViewPort);
	 float ScreenCenterX = ( float )gViewPort.Width / 2;//Horizontal Position
     float ScreenCenterY = ( float )gViewPort.Height / 2;//Vertical Position
	 
	D3DRECT rec0 = {ScreenCenterX-9, ScreenCenterY, ScreenCenterX+ 9, ScreenCenterY+1};
    D3DRECT rec1 = {ScreenCenterX, ScreenCenterY-9, ScreenCenterX+ 1,ScreenCenterY+9};  
    Device_Interface->Clear( 1, &rec0, D3DCLEAR_TARGET, D3DXCOLOR(0, 0, 0, 1.0), 0,  0 );//black
    Device_Interface->Clear( 1, &rec1, D3DCLEAR_TARGET, D3DXCOLOR(0, 0, 0, 1.0), 0,  0 );

	D3DRECT rec2 = {ScreenCenterX-8, ScreenCenterY, ScreenCenterX+ 8, ScreenCenterY+1};
    D3DRECT rec3 = {ScreenCenterX, ScreenCenterY-8, ScreenCenterX+ 1,ScreenCenterY+8};  
    Device_Interface->Clear( 1, &rec2, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 1.0, 1.0, 1.0), 0,  0 );//white
    Device_Interface->Clear( 1, &rec3, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 1.0, 1.0, 1.0), 0,  0 ); 

	 D3DRECT rec4 = {ScreenCenterX-7, ScreenCenterY, ScreenCenterX+ 7, ScreenCenterY+1};
    D3DRECT rec5 = {ScreenCenterX, ScreenCenterY-7, ScreenCenterX+ 1,ScreenCenterY+7};  
    Device_Interface->Clear( 1, &rec4, D3DCLEAR_TARGET, D3DXCOLOR(0.62745098, 0.125490, 0.959999, 1.0), 0,  0 );//purple
    Device_Interface->Clear( 1, &rec5, D3DCLEAR_TARGET, D3DXCOLOR(0.62745098, 0.125490, 0.959999, 1.0), 0,  0 ); 

    D3DRECT rec6 = {ScreenCenterX-6, ScreenCenterY, ScreenCenterX+ 6, ScreenCenterY+1};
    D3DRECT rec7 = {ScreenCenterX, ScreenCenterY-6, ScreenCenterX+ 1,ScreenCenterY+6};  
    Device_Interface->Clear( 1, &rec6, D3DCLEAR_TARGET, D3DXCOLOR(0.0, 0.0, 1.0, 1.0), 0,  0 );//blue
    Device_Interface->Clear( 1, &rec7, D3DCLEAR_TARGET, D3DXCOLOR(0.0, 0.0, 1.0, 1.0), 0,  0 ); 

    D3DRECT rec8 = {ScreenCenterX-5, ScreenCenterY, ScreenCenterX+ 5, ScreenCenterY+1};
    D3DRECT rec9 = {ScreenCenterX, ScreenCenterY-5, ScreenCenterX+ 1,ScreenCenterY+5};  
    Device_Interface->Clear( 1, &rec8, D3DCLEAR_TARGET, D3DXCOLOR(0.0, 1.0, 1.0, 1.0), 0,  0 );//cyan
    Device_Interface->Clear( 1, &rec9, D3DCLEAR_TARGET, D3DXCOLOR(0.0, 1.0, 1.0, 1.0), 0,  0 );

    D3DRECT rec10 = {ScreenCenterX-4, ScreenCenterY, ScreenCenterX+ 4, ScreenCenterY+1};
    D3DRECT rec11 = {ScreenCenterX, ScreenCenterY-4, ScreenCenterX+ 1,ScreenCenterY+4};  
    Device_Interface->Clear( 1, &rec10, D3DCLEAR_TARGET, D3DXCOLOR(0.0, 1.0, 0.0, 1.0), 0,  0 );// green
    Device_Interface->Clear( 1, &rec11, D3DCLEAR_TARGET, D3DXCOLOR(0.0, 1.0, 0.0, 1.0), 0,  0 );

    D3DRECT rec12 = {ScreenCenterX-3, ScreenCenterY, ScreenCenterX+ 3, ScreenCenterY+1};
    D3DRECT rec13 = {ScreenCenterX, ScreenCenterY-3, ScreenCenterX+ 1,ScreenCenterY+3};  
    Device_Interface->Clear( 1, &rec12, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 1.0, 0.0, 1.0), 0,  0 );// yellow
    Device_Interface->Clear( 1, &rec13, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 1.0, 0.0, 1.0), 0,  0 );
    
    D3DRECT rec14 = {ScreenCenterX-2, ScreenCenterY, ScreenCenterX+ 2, ScreenCenterY+1};
    D3DRECT rec15 = {ScreenCenterX, ScreenCenterY-2, ScreenCenterX+ 1,ScreenCenterY+2};  
    Device_Interface->Clear( 1, &rec14, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 0.549019608, 0.0, 1.0), 0,  0 );// orange
    Device_Interface->Clear( 1, &rec15, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 0.549019608, 0.0, 1.0), 0,  0 );

    D3DRECT rec16 = {ScreenCenterX-1, ScreenCenterY, ScreenCenterX+ 1, ScreenCenterY+1};
    D3DRECT rec17 = {ScreenCenterX, ScreenCenterY-1, ScreenCenterX+ 1,ScreenCenterY+1};  
    Device_Interface->Clear( 1, &rec16, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 0.0, 0.0, 1.0), 0,  0 );//red
    Device_Interface->Clear( 1, &rec17, D3DCLEAR_TARGET, D3DXCOLOR(1.0, 0.0, 0.0, 1.0), 0,  0 );
     
	   
}
sorry a little messy
basically what this does get your current viewport(monitor/display) then draw a rainbow crosshair at the center coordinates of your screen given by ScreenCenterX and Y each divided by 2

to prevent any leeching ill not tell you how use this unless u ask nicely and dont be a choob/scriptkiddie

pro coders should be able to figure out themselves very easily :P

EDIT:
sorry why06 can you change the title of this post to Rainbow Crosshair Function?
typo lol