NOTE: With this code you ae messing with the programming of the game. You might screw the whole thing up if you're not careful.
To get better resolution find the folder that TIBERIAN SUN is in, double click on the folder and find a file called SUN.ini, open it and go down to where it says [Video]. In that you should see somthing like this:
ScreenWidth=
ScreenHeight=
StretchMovies=
go to ScreenWidth= and change the number to: 1024 then go to ScreenHeight= and change the number to: 768, finally go to StretchMovies= and enter: no
This will only work if the max resolution on your monitor is 1024 x 768 or higher.