Working in the service menu on the older Toshiba projection TVs is not too difficult, you just have to take everything slowly, write down what settings you have before you change them, do not adjust parameters just because they look interesting (!) and TAKE CARE!!
The Keohi web site will explain how to get into service mode. Once you are there you can do two things.
1) Adjust a whole load of parameters of the TV. Most of the time all you need to do for a simple overscan adjustment is to use the HDnet test transmission, if you have an HR10 or HR20 you can record it and then use it any time you like. You adjust horizontal and vertical position, and height and width, to make sure your picture is centred and there is not too much overscan. Write down what all the settings are before you change them, so you can change them back if you screw up. This web site
http://www.smartcalibration.com/hdnetpatterns.html should also be useful.
2) In service mode you can also adjust convergence parameters at the corners of the screen, correct for common distortions, and do a full convergence adjustment, which allows you to do a very precise alignment of the red, green and blue guns on each of the TVs inputs. To do this properly you really need an overlay grid which shows you where all the grid lines on the TV need to be. This is what the professional calibrators do. Doing a correct full convergence can take a long time, going backward and forward adjusting the three separate colors across the whole screen , in antenna, video 1,2,3 and Colorstream (component) 1 and 2 (that's what I have on my TV). Even a professional calibrator can take all day just doing a few inputs.
I need to stress that although going into service mode gives you the ability to set up your TV's overscan and convergence accurately, it also allows you to set all sorts of other parameters which are NOT for the amateur. So I carry no responsibility for any problems you create while you are in service mode. There are even a couple of parameters that if you set them incorrectly the only way to get your TV working again is a service call.