[oicq747285250]

the function ShowPlayerWritingDialog(playerid, dialogid, text[])
strlen(text) to get the text length
then
make a timer
SetTimer("SpecialShowPlayerDialog",speed,1,"ddds", playerid, dialogid, style, text);

function SpecialShowPlayerDialog(playerid, dialogid, style, text[])
{
len++
ShowPlayerDialog(i,12350,DIALOG_STYLE_MSGBOX, "", text+text[len],"OK","CANCEL");
}