I set up the Ultimate SiN Patch and from what I understand, it's set up for 1920x1080 which is my monitors native resolution. However, when the game starts, it flickers like crazy, as if the frequency is off, but I see no way of adjusting it.

Have you tried the Sin Patcher from http://sin.nanoaugur.net/? I tried Ultimate SiN patch at first but I still had problems with the game so I went to PCGamingWiki and the Sin Patcher fixed the game for me.

1. Download a Sin Patcher for either 1.11 retail or 1.12 Steam.
2. Move it to the installation folder and run it.
3. Type in your desired resolution values and click Apply resolution.
4. Start a game and select 1152x864 resolution in game's options.

(Info taken from https://pcgamingwiki.com)

Thanks, but this didn't help. With this, the game goes into a black screen. I have to alt-tab several times to close it, sometimes even bring up the task manager to close it.
I have a Radeon 550 4gb card and 6gb ram Win7

Maybe try changing the gamma setting in nGlide? It seemed to work for other people.

I had the same problem with this game my game would run but with a black screen but you can hear the game in the back ground I fixed it by going in to nGlide and do the following you have to do it all like this or it will not run SCREEN RESOLTION set it to by desk top.ASPECT RATIO set it to 4:3. REFRESH RATE set it to 120HZ. VERTICAL SYNC HORNIZATION set it to on default. GAMMA CORRECTION set it to 0.7 3DFX LOGO SPLASH SCREEN set it to on default and save the changes and launch Sin Gold hope this fixes your game Have a great weekend.