As others pointed out, finding Win98 drivers for that will be quite a challenge. The same probably applies to Windows 2K/Me. If for some reason you don't like XP, a good alternative for T43 is OS/2 based OSs, starting from 0S/2 Warp 4.52. I tend to prefer supported and maintained software as long as the device is expected to surf the internet, so ArcaOS would be a better alternative.

Linux support for 32-bit x86 is shriking day by day; at this point you'd better install NetBSD on anything i486 onward (but this is just my opinion).

I'm using irssi as well (would a thread about irssi plugins be worth?). Before that, epic5