Just wondered if many have an old windows msdos/95/98 or XP computer based on sub 1ghz processors and old graphics cards they use for running old PC games. Seems like a lot of great classic PC games have disappeared and can't be run easily on the latest hardware. 

What is the best way to play classic PC games from the past?

Depending on your exact needs, DOSBox or a virtual machine with an older Windows version might suit your needs. Mind you, virtual machines might have limitations in regard to 3D, but they might work well enough for older stuff. It's easy to try, so it shouldn't hurt to try.

I used to have trouble running PC games on actual PC's. I was also mucking about trying to create more base memory so a game would run. Some of my favourite old pc games were tricky to get stable.

I have one with 433MHz Celeron and Voodoo2 16MB graphics card if I'm not mistaken. Haven't used it for a long time. But still, it is a pretty cool setup to play retro PC games. I've used mine for Duke Nukem 3D, Quake, Doom, Soldier of Fortune and other 90s games. So, if you can afford to build such rig I think that will be the best way to play retro PC games.

Yeah, I use DOSBox myself, but as it is emulation, there will always be issues. I do know at least one person on this site that has a DOS-based PC though.

I imagine DOSBox works for the vast majority of cases but in case it doesn't, you could always try FreeDOS or MS-DOS in a virtual machine. Virtual machines have their own issues, but it's possible they could circumvent the problems caused by emulation. If you need an actual DOS machine though, I imagine it's not going to be fun these days. Setting up dual-boot on an existing machine doesn't sound fun, and having a separate computer just for DOS sounds pretty impractical. Of course if someone likes that, who am I to judge them.