Cleanup.
Unless you have clean copies don't make assumptions based on non-official versions.
To play without the Steam DRM:
<= v5135 using Revemu or SteamEmu (not Smart Steam Emu)
> v5135 use CLI switches
You can try using the hl2.exe from v5135 on older versions and see if that works if too lazy to copy the revemu steam.dll over. Unknown if that would affect OS compatibility or not for 98 and 2000 if it works, it's likely it would. For 98-ME you'd likely have to use KernelEx with revemu, possibly an ancient SteamEmu version might work.
Build OS compatibility:
v7122284+ = Vista (Haven't tested Vista with newer builds in a while)
5135-v5377866 = XP
4295-5135 = XP+
2455-4104 = XP
2152-2217 = 98-2000