I'm not sure what you could hope to accomplish that couldn't be done with free materials, like the aforementioned AVS HD 709. If you don't own a colorimeter, then there is very little that you can do to accurately calibrate a TV, and the U50 has very little in the way of adjustment anyway. Without a meter, about all you'll really be able to do on a U50 is set basic stuff like brightness and sharpness (which are really not that difficult to set even without a calibration disc). With a meter, you would also be able to enter the service menu and adjust the color balance controls. You can set color/tint just by eyeballing the TV -- if you aren't taking any measurements, then I don't see how a calibration disc would be helpful with grayscale or color.
If you want the best image quality on your U50, then follow the advice of others (by putting it in cinema mode with contrast at 100, color temp at warm 2, sharpness at 0, etc.). Use something free like AVS HD 709 to set the brightness, which probably needs to be at about 56. Color probably needs to be set below 50, and you can just eyeball the TV to set that -- put color wherever skin tones look the most realistic, unless other colors then appear noticeably undersaturated, in which case you may want to settle for skin tones appearing a little oversaturated. And if you want more accurate color beyond that, then buy a colorimeter and use it to adjust grayscale and check color/tint.
In my own calibrations, I use my own images created in Photoshop to adjust color on TVs with a CMS, and I use AVS HD 709 for everything else (grayscale, etc). I've owned retail calibration discs in the past, but I really don't find them useful anymore.