I'll assume your not sharing illegal content, so.. You can use the following which will PREVENT the message window opening if it starts with 'XDCC SEND' and instead notice them to type the /ctcp command instead.
On ^*:Open:?:{
if ($1-2 == XDCC SEND) { .notice $nick Please use, /ctcp $me $1- | haltdef }
}
Eamonn.
