As far as I know this has been tried before. But as the "itemdrop" sound is played whenever gems, city scrolls, skillbooks, tokens, arrow packs and quest items like on halloween drop, all those items would drop with met/DB sound too.
So, it isn't done with changing the sound file.
But, if memory serves me right, wasn't there a way to change a file so that at least gems (along with city scrolls and some others) would drop with an other sound. I think something like that was posted here some months back.
If you don't mind having city scrolls drop with a jingle, go to conquer2.0\sounds, copy the bell wav, paste it in the same folder, rename the dropitem.wav to, like, dropitem.wav.bak (as a backup), and rename the copy of bell.wav to dropitem.wav. Or find a soundfile you like, copy it to the sounds folder and rename it to itemdrop.wav.
Edit: BTW, there is even a gemdrop.wav, but someone seems to have been to lacy to actually use it.