The ballast is seperate from the light engine, but is mounted ON the light engine.
The 'shadow' indicates a bad LIGHT TUNNEL ONLY. In order to have Toshiba replace/rebuild it, you will have to call them, they send out a tech to verify a shadow (which you don't have) and then they do their thing. If you don't have a shadow, I wouldn't sweat it myself.
Stuggling to light and not lighting are 2 different things. While the ballast could certainly be bad, it could be as simple as a lamp itself going bad. In my opinion a DLP owner should ALWAYS have a NEW, spare lamp, just in case. If you have one, you should try a swap and see if that doesn't fix things first. If it doesn't, turn your attention to the ballast. Even if you need to buy another lamp AND locate a replacement ballast, it is still a helluva lot cheaper than getting another TV. And in my opinion, these sets are just fabulous and worth keeping going. SHould you need your ballast replaced/repaired, I suggest you go here:
http://www.moduslinkptstvboards.com/75002433-P6058.aspx
Spare lamps I have tried a few places but like Laptops for Less as the best quality/price ratio.