I got it working and it's GREAT!
The screen is wide enuff to have 2 side-by-side windows open without overlap. You can see wide pictures without having to shrink them to unsatisfying vertical size. And I added a second screen to put the file window, tools, and layers for Adobe Photoshop on, leaving the entire picture unobstructed!
Long post, but hopefully, this post will save some future widescreen purchasers with old Dell computers a bunch of time and frustration and maybe it will work for other brands.
If you Google 'Dell Optiplex widescreen' you will see alot of people looking for help, but not many posts saying their problem is solved. I was surprised to see this problem going back to the early 2000s! Apparently, there were wide format monitors before HD TV. I didn't find anything that was specific enuff to help me.
One thing to keep in mind here is that I do not have the Optiplex connected to the internet. Windows is like The Bubble Boy - no immune system! It works fine as long as it is isolated from the environment, but put it online and, between Microsoft 'updating' it and a virtual swamp of malware, it will gradually degenerate into a useless hulk. All the McAfee, Norton and other brand security software can only delay it and will slow everything down from the moment you install them.
Around 2012, I got my previous computer, an Optiplex 755 and also got a Toshiba NB505 netbook specifically to get on the web. Both had Win7. The NB505 worked great at first, but after about 4 months, had slowed to a crawl. The usual history clearing and defragging didn't help, so I did a reformat. That helped alot, but is a major hassle, even with having hardly anything on the computer. Over the next 2 or 3 years, this cycle repeated several times. At 1 point, after getting a blue screen ransom attack, I reformatted and even put Norton on it. (about 50 bucks!) It was never like new after that. Slow, and always having things interrupted by Norton.
But eventually, it got so slow, even after complete reinstall of the OS, that I gave up and tried putting a Linux OS on it. Not being a software nerd, it did not work out well for me. It could sorta access the internet, but everything was very basic and crude looking. Some websites wouldn't even open. By then Google Chrome was available so I got a Chromebook.
Meanwhile, the Optiplex 755 was perfectly healthy. Maybe once or twice a year I did a defrag, but that's it. And it stayed that way till a few months ago. (August 2020) I'm totally digressing here, so I'll shorten the story of what happened to: I got another Optiplex 755 with Win10 on it and connected both of them to the same monitors and keyboard. Either the Win10 (connected to the internet) killed it thru the connections or the Vizio TV somehow zapped it thru the HDMI cable. I still don't know. Evidence for both theories.
All this is to say that part of the problem of getting a video driver to install is because the machine is not connected to the internet. There are a variety of Windows things that need to be updated in order for the video card drivers to install and work.
To help with Google searches, I will restate some of the basic info:
I have a Dell Optiplex 760 with Win7 Pro 64bit and got a new LG 29WK50S, which is a 21:9 ultrawidescreen computer monitor. (29", 2560 x 1080) It came with a disc, which you would assume has the driver on it, but does not. It only has safety warnings, warranty info and legal junk. A complete waste of time, don't bother sticking it in your player. And don't bother going to their website. No help at all.
After many wasted hours, I gave up on the Radeon 5450 video card and got a PNY NVIDIA Geforce GT 730. It came with a disk that had the driver and other software, but also failed to install. It would get to the point where you restart the computer and during boot up, Windows reinstalls the standard driver which blocks the new driver from being installed.
So, I went to the NVIDIA website and got the most recent driver for the GT 730. There was also something from Microsoft, NT 4.0, that I supposedly needed and got that. Still no driver install. Another 2 hours wasted.
I gave up for a few days. I have a much more important project to work on. (I'm making UVC pathogen killer helmet and face mask prototypes).
When I got back on it, I tried installing the most recent 2020 Geforce driver, even tho it wasn't listed as applicable to the older 'legacy' GT 730. It got farther, but still failed. I tried a few more times but finally decided to risk connecting the computer to the internet.
That worked.
It automatically downloaded a bunch of stuff from Microsoft and NVIDIA, then restarted with the LG ultrawidescreen at its proper 2560 x 1080 rez. And the old ViewSonic screen was on now!
I immediately pulled the internet cable out.
The conclusion is that if you want to use a widescreen on a Win7 computer, you are going to have to risk some updates from Microsoft. I have heard many stories of them 'Win10ifying' older OS versions, forcing people to lose older software and have to be on the web, so be careful. My ancient edition of Adobe Photoshop, for example, will not work in Win10.
In my opinion, LG gets the lion's share of blame for this, considering that it's their product that needs to work with the hardware that's out there. I imagine they must be getting a bunch of returns from disgruntled customers. They did a great job on the hardware, but dropped the ball on the software. Actually, they never even picked it up!
Maybe AMD can take this as an opportunity to develop a universal driver package that works for a wide variety of configurations and situations. I would have gladly payed 20$ for such a thing to save myself a barge load of time.
