Aye, that's kind of why I pretty much gave up on PC gaming about 17 years ago, couldn't get anything to work under Windows XP.
I'm going to sorta echo what Joshua said.
The machine you're describing is... well, it's not JUST that it's old. It's that it's from a whole different era. Game specs dont really work the same way they used to. Back closer to 2000, games were alot more... "picky" about your specs. I'm not sure how else to put it.
That has changed though. Now, alot of games will run even on weaker machines. Hell, a friend of mine has a PC that he's had for 2-3 years now, and it was a pretty weak machine to begin with... some low-end thing bought at the freaking Best Buy of all places. He cant afford an expensive one, so, low-end it was. BUT. It will still run most modern games fine. It wont run them at super high settings, but it will indeed run them, and the framerate will be okay. Contrary to what alot of gamers will tell you, you SERIOUSLY dont need to be running games at max bloody settings all the time. Particularly nowadays, when even at lower settings, many games still look great.
Now, there are some exceptions. For example, a machine like his would flip out if he tried to do virtual reality with it... THAT is much too intensive for a machine like that. But normal games, on a normal monitor? No problem!
Not to mention that games have just become easier to run these days. I remember back around 2000, just dealing with these bloody machines was.... so much more unnecessarily complicated. Now, any game from my list is just a couple of clicks away. I may have a blazing hatred for Windows in general... but I cant deny how much easier even that is to use these days. It's actually become easier and faster to use than the consoles (when it used to be the other way around). Takes bloody ages to get any console game started, compared to the "right freaking now" of any remotely recent PC. Even better with an SSD... I dunno how I ever got along with a traditional hard drive.