This is turning in to a serious script =)

Revised version will give you a right click nick and channel menu option to search in the channel buffer or log file. The channel menu also has the option to search in any file.

Code:
menu nicklist {
  -
  Search
  .#: search # $1
  .# log: search @log # $1
}
menu channel {
  -
  Search
  .#: search # $?="Search key:"
  .# log:  search @log # $?="Search key:"
  .Any file...: search @any $?="Search key:"
}
alias search {
  window -k0z @SearchResult -1 -1 $calc($window(-2).w * .75) $calc($window(-2).h * .75)

  if $1 == @log { 
    var %fi = * $+ $replace($3-,$chr(32),*) $+ *
    var %fn = " $+ $readini($mircdir $+ mirc.ini,n,dirs,logdir) $+ $mklogfn($2) $+ "
    if $isfile(%fn) { filter -fwcp %fn @SearchResult %fi }
  }
  elseif $1 == @any { 
    var %fi = * $+ $replace($2-,$chr(32),*) $+ *
    var %fn = " $+ $sfile(*.log) $+ "
    if $isfile(%fn) { filter -fwcp %fn @SearchResult %fi }
  }
  else { 
    var %fi = * $+ $replace($2-,$chr(32),*) $+ *
    filter -wwcp $1 @SearchResult %fi 
  }
}