This is font dependent.
The tab key (ascii character 9) will show properly if the correct font is used. The most common fonts will show it correctly, so you are either using a font that is not one of the most common (ie: not Fixedsys or Times New Roman)

Note: I only named two fonts, but there are a lot more. The two I named are the two I use on a regular basis, and I have no problems with any of the characters showing incorrectly.

If the person sending you the information sees it correctly, you should find out which font they are using.

On the other hand, if they are sending it to you as a text posting, rather than via a DCC'd file, you might try this code.

Code:
on ^*:text:*:*:{
  if $chr(9) isin $strip($1-) {
    echo $iif($chan,$v1,$nick) $replace($1-,$chr(9),$+($chr(32),$chr(2),$chr(32),$chr(2),$chr(32)))
    haltdef
  }
}


Note: This code was generated on the spot, so I don't guarantee that it will work, but the theory is sound.