For verson 1.3 you need to have a save file present and an unprotected executable.
Open "dmc3se.exe" with a HEX editor. Search for...
AA AA AA C1 E2 02 F7 E2 D1 EA 3B CA 74 0C C7 06
80 02 00 00 C7 07
E0 01 00 00 5F 5E C3 90 90 90 8D 44 24 08 8D 4C 24 04 50 51 E8 B1 FF FF FF
Change the bolded values to your desired widescreen resolution. Remember to flip the order.
Using 1920x1200 as an example...
AA AA AA C1 E2 02 F7 E2 D1 EA 3B CA 74 0C C7 06
80 07 00 00 C7 07
B0 04 00 00 5F 5E C3 90 90 90 8D 44 24 08 8D 4C 24 04 50 51 E8 B1 FF FF FF
Then open up your sav file(s) with a HEX editor. The format for the files is "save#.sav". Scroll to the bottom of the file and scroll up until you find a non-zero value. This will be the current resolution value you have selected in-game. For example a 640x480 resolution...
00 00
80 02 00 00
E0 01 00 00
Change these values to match the resolution you added in the first step. 1920x1200 example...
00 00
80 07 00 00
B0 04 00 00
Done. Stretch.
