Windows XP with Service Pack 2 would run great.

I can't speak in regards to a K6-2 500, but for a few years in the RadioShack store I worked for, I was running XP on an early industrial tablet computer (Fujitsu Stylistic LT C-500) equipped with a Celeron 500, 256MB RAM and a 160GB hard drive (I do not know if the drive controller supported ATA66 though). It was quite horrendously slow for me, but granted a lot of that slowness was likely due to the Celeron processor, as well as overhead from the touchscreen utilities and RadioShack ICS/POS software. That said, it was just barely within my personal definition of "usable", although my patience with slow computers tends to be a fair bit more lenient than others (my coworkers absolutely loathed that system).

Ten years ago, I did (temporarily) install XP on a K6-2 350 system with 96MB RAM, don't recall the hard drive size. It too was quite slow, I'd say comparable to the Fujitsu tablet during the rare instances when it wasn't constantly hitting the pagefile. I would not consider that system usable though simply because of how heavily it was bogged down by pagefile hits. From my experiences, even vanilla XP requires an absolute bare minimum of 160-256MB to be realistically usable, with 512MB being the sweet spot for XP with SP2.

Thus, assuming it's not running any unnecessary programs and is properly optimized, it should be easy to make such a system usable for your stated goals.

Ran XP SP1 just fine on both a Pentium 166 MMX (Though this was a very minimal install used as a temporary IIS server) and a Pentium II 266 around 2006-2008, with 64MB and 128MB RAM I think, both seemed to run as well as they needed to.

I seem to think I severely altered the OS though, removing themes, visual effects, high color icons and a few other things to get as much speed as possible. The little MMX was noticeably hesitant at times though and would occasionally take a while to serve pages, rattling the hard drive - one of those disgusting 8GB Seagate Medalist things - causing violent sounds of death to emanate from the closet. It was a µATX system with a SiS 530 based PCChips board, Including a stupid PSU with PCChips branding (PC100) which smelled strangely of burning until it stopped working a few years later. This system started life as a standard Hull school computer, still have the case with my schools anti-theft branding on it, and strangely, it started out with a K6-2 that I was using elsewhere by then (i.e. in a better board)... Umm... I won't go into how I acquired it, but lets just say that when I got my hands on it in the latter half of 2005 I was still at school and at my school, there was a rule among the students; Anything left it the corridor was first come, first served. This included tables, chairs, drugs, booze, porn mags, guns, windows, floor tiles, radiators, knives, light bulbs and a few other things.

The Pentium II was generally fine until one fired Opera up, but the ATI Radeon 9200 and the small alterations to the OS helped. Games did run better in 98 though, as they always did, but the system was certainly usable, only leaving daily use a few years back after getting some upgrades and starting to fall apart... It was a scrap build, my first Pentium II, and it lasted a long time all things considered.

Stojke wrote:

Windows XP with Service Pack 2 would run great.

It would run on the "barely acceptable" side of things. 😜

Ran XP for years on a K63-400 with 384MB of ram. Ran fine.