A 200MHz PC with 1Mb of video ram and Win95 should be enough to make for a useable WinUAE setup at A500 speed, and should take no longer than an A500 to boot into Workbench (ie. about 20 - 30 seconds). I was doing that in about 1998, quite happily!
I have an ATI Rage 128 Mobility in my laptop, it runs everything at 1400x1050 rock solid, including WinUAE (DirectX heavy games run at 1024x768 happily). Old VIA chipsets generally run fine under Win98, I've certainly never had any problems.
While this chap's setup may be old, it's nice to see some recycling of old equipment. While it's working it can be useful to someone, all it means you have to choose software to suit the age of the PC - just think back to when 400MHz was rippingly quick - not all that long ago ;-)