Can mIRC display Tab character properly? If not, can it rather convert it to spaces? And not just substitute it with 8 spaces (or 4?), but actually calculate how much is needed (between 0 and 8).

Actually, it would be nice if mIRC allowed you do that, and set tab width (to 4 or 8) in Options. And also maybe option to convert tab to spaces when sending messages, so other clients who cannot display tabs can see spaces instead.

Have a look at the thread here.

Eamonn.

Absolutely nothing to do with this.
If you are suggesting I should replace tabs myself via a script, then its wrong.
This should be a native mIRC feature.
I can do identd via a script, yet its a native feature.