Does anyone here use a dual boot system (for example, Windows 7 & Windows 10)?
Or a virtual machine (running different OS's)?
Are there problems with using a newer graphics card (that doesn't support Windows XP or 7)?
Some older games don't play on Windows 10, even in compatibility mode.
I dual Boot Windows 10 and Linux Parrot. There can be some issues. If you use the same hard drive Windows will try to override the other installation by removing the dual boot option, cause Windows wants to be the only OS running. If you install Windows first, then another OS, it should be fine. At least if the second install is Linux. Not sure how Windows handles another Windows install on the same hard drive. Regardless, it is possible depending on the two Windows OS you want to install.
However, if you install Windows on one drive, then disconnect that drive. Then install Windows on a second drive, then connect them both back up with the SATA, you would be good.
Now, that's in theory, cause there are MANY more things to consider besides a GPU and how many hare drives you need.
It sounds like you want to Dual Boot modern Windows & XP?
1. Windows XP has 2 versions. 32-bit and 64-bit. XP-64 is trash if you intend to use this for XP gaming. And 32-bit, is well 32-bit. I can't imagine things would go smoothly, but you never know. Depends on the motherboard, and if it has an XP compatible chipset.
2. RAM: I think XP-32 with Service Pack 3 has a 4GB RAM limit. I think you can install more, but I probably wouldn't recommend it.
3. CPU - It is desirable to run XP on a single core. You could disable any extra cores in Windows though.
4. Soundcard - XP is an era that still benefits greatly from a quality sound card, such as a SoundBlaster X-Fi. You really want EAX sound for those old XP games. There are custom drivers though for old X-Fi and Audigy 2 ZS cards on this guy called "Daniel K" website.
Now that I think about it, I think the GPU is the least of your worries.
If you are looking to build an old XP machine, I bought a bunch of Old PC stuff from a guy recently. I could sell you one super cheap, bit would be expensive to ship. You can build an XP system super cheap right now. For less than the cost of an old Windows 98 Voodoo GPU. It's a good time to build one of you want one.