GeForce 6 is a no-go for Flash GPU; here's the list from nVidia:
http://www.nvidia.com/object/gpus_supporting_adobeflash.html
And remember that Flash GPU is not 100% acceleration; it's "acceleration assist" - Tom's explains it well here:
http://www.tomshardware.com/reviews/adobe-fla … ion,2805-4.html
So depending on what you want it to play, it may or may not work properly even with a GeForce 8 or higher (you'll still "feel" the older CPU, lack of SSE2, etc). There should be nothing to worry about with DX10 not being supported though (there shouldn't be any "working at a disadvantage" - plenty of people used (and probably continue to use) GeForce 8, 9, 200, etc (and Radeon 2/3/4k etc) cards under XP for years with no ill effects and no DX10 - as long as you don't want to play DX10 games that is). Support for those cards under 98 may be another question though, as Shagittarius pointed out.
The Radeon will likely do you no good either; AMD doesn't support Flash GPU on lower than Catalyst 9.11/Radeon HD 4000 series (Adobe's "line" is: "essentially the same as Windows Vista with Aero Glass" to support Flash GPU on Windows (https://blogs.adobe.com/penguinswf/2008/05/fl … es_the_gpu.html)). You may have somewhat better luck with Flash GPU on Linux, but I still wouldn't expect killer performance. Regarding the X1950 specifically - keep in mind the relatively high power requirements of such a board, most of which will be on the +12V rail of your PSU. You'll also have to find an AGP variant - most of those cards are PCI Express (and don't be surprised to see the AGP cards with hilariously high prices as salvagers try to take advantage of folks with old machines).
In general I'd say that "realism" is probably the key here - either the machine can be a killer Windows 98 gaming system (sounds like it already is!), or it can run 2000 or XP with newer graphics hardware and still struggle with various multimedia web tasks (honestly the modern web is just too bloated for such a machine, and HD probably will never be on the table for it), as well as the ever-present security concerns still associated with an unsupported operating system.
From personal experience, a 1GHz P3 with a WildcatVP (uses the Xorg basic VGA drivers) running Puppy Linux (Wary 5.5) was/is okay for basic browsing (you can view sites like Vogons without any problems, but something heavy like YouTube or Netflix is likely to be a no-go; don't even think about HD). I would consider it acceptable as a hold-over or part-time machine for multi-boxing or something like that; it really had no issues with mostly text sites. As far as memory demands, my P3 box "only" has 384MB of memory, and had plenty available even with Puppy booted - with your setup with 768MB you should have zero concerns unless you want to open up (and never close) a ton of applications.
My advice would be to go one of two routes (I guess you could do both if you want/need multi-box capability):
- Use Wary Puppy for web browsing; it'll just require a bootable CD/DVD or flash-drive and will let the machine stay "stock" with Windows 98 for when you want to game. Seems to be less hassle than configuring a multi-boot environment as well. More info about Puppy is here: http://www.puppylinux.com/ (and I suggest Wary Puppy because it's what the developers suggest for older machines)
- If you have the resources, build or acquire a newer machine that can run a newer operating system (like Win 7/8, OS X Mavericks, Ubuntu 14.x, etc) and has a modern processor and graphics controller (even a modern Celeron with the HD IGP will be suitable for modern multimedia and browsing) which will make for a faster/smoother/better browsing experience and still preserve the Win98 box for gaming (and doesn't open it up to all of the bloat and security headaches associated with running 9x or 2000/XP on the modern web).
Another, somewhat perverse option:
- With some minor upgrades your system could technically meet the minimum system requirements for Windows 7 (it would need another 256MB of RAM, may need another hard-drive (depending on how much space you have), and a graphics card that supports WDDM/DX9). I don't want to imagine how sluggish it may be, but if you had a more modern gcard in there it might just work to dual-boot with 7 and 98 - the biggest question is then finding a card that will play nice with both Windows 98 and Windows 7. I've read that GeForce FX has a WDDM 1.0 driver (nVidia lists 96.85 on their website), but have never personally tested it. Might be something to look into.
Very cool machine by the way! How do you have the video routed for all three 3D setups? What does it do for audio? (oh, and it looks like some of your images on the other thread are dead 😢)