Read the TV manual and find the resolution supported by the d-sub (15 pin) port. Set the video/graphic output to that resolution.
Be aware that it will NOT be the resolution of the TV and I'll guarantee the picture will not fit the screen. For full view you need to use an S-video connection or HDMI.
Don't ask me how I know.
I tried to connect my hp computer to my Samgung tv using the 15 pin, however, the tv stated that the signal was not found or not compatible. would you give me some better instructions for hook up so i can watch movies throught the tv?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic