You could offset the sprites UV's to only show a part of it's texture, then size it to how you want it
or
you could GetImage on the part of the sprites image that you want and paste it, I guess it would depend on what you want to do with it, for just a health bar, I think pasting should work aswell as using a sprite.
If you can, can you post a pic of your HUD, when you said health bar that isnt a straight line, you have me all curious now lol HUD graphics and interface ideas are something I need to start looking at soon myself
If it ain't broke.... DONT FIX IT !!!