Actually, "best" would be to read the docs, look for examples, etc. There've been a lot of posts here on gamedev about similar problems.

Thanks man. But, I have actually been reading up on this for days and days now, with no huge progress.

I actually got it behaving correctly just then by changing my LockedRect call to this...

hr=mRenderer->textureVideoGet()->LockRect(0,&lockedRect,NULL,0);

...making the third parameter NULL (the area to lock). So, I guess I am now locking the whole image? Not sure why it doesn't work if I specify a rect though. Odd.

But, I am now seeing a 5 pixel white line (as intended).

Using D3DPOOL_MANAGED is nice because when you reset your graphic (fullscreen ->windows, change resolution...) you dont have to worry about the Texture. Otherwise you will have to relase and recreate all the texture you loaded!