tburger: Right now I'm in the process of upgrading my VERY old PC. I hope to leave XP and get Windows 7 instead and possibly upgrade CPU. I see Core2 Duo that cost less than EUR 10 and outmatch my Pentium D twice. If I succeed - it should be be enough for another 5 years :-P
If you want to stick with Socket 775 for a little bit more, then I suggest getting a Core 2 Quad, the Q6600 goes on ebay for about 15e. As a CPU it isn't much today but it will let you play many games including some recent ones, just don't expect high details or 1920x1080 resolution.
I keep an old system at home with a: Core 2 Quad Q6600, 5GB DDR2 Ram, Nvidia GT 1030, Crappy 320GB HDD
Occasionally I test a few games on it, the ones I tried are Space Pirates and Zombies 2, Yooka Laylee, Divinity Original Sin, Signal From Tolva, Hollow Knight, Hand of Fate 2 - they all run very well at 720p medium details.
And of course, does it run Crysis? Tested that too, Medium details, 720p, FPS jumps between 25-45fps.