I get that going forward, with GOG Galaxy not supporting Win XP, that they're not listening games for Win XP, but I'd like to play it on my Retro PC :(. I'd like to buy the game, but... if buying it makes it so I can't play it, then... I'm just wasting money.
I can confirm that both NecroVisioN and NecroVisioN: Lost Company* work on XP SP3. :)
In fact, of the two shortcuts that are created in the Start menu folder the one that says 'NecroVisioN (dx9)' points to 'NecroVisioN.exe', while the shortcut that simply says 'NecroVisioN' adds a command line parameter for dx10 and so it points to 'NecroVisioN.exe +dx10'.
In addition, both games make use of EAX which works natively in XP and works perfectly on my retro X-Fi card. :p
In other words, while the games came out during the transition away from XP, EAX, and DX9 to Vista and Win 7, and are only supported by gog on the latter systems, they were made foremost for XP and should work best on your Retro PC. :)
*NecroVisioN: Lost Company woudn't load because of a missing DX10 .dll so in the config.ini in the Bin folder I edited Cfg.RenderDevice = 2 to Cfg.RenderDevice = 1 and boom it worked.