This should work. msg_type for SayText is 3 in CS:S. The format is:
Code:
pWrite->WriteByte(OwnerIndex);
pWrite->WriteString(message);
pWrite->WriteByte(bChat);
as you can see in the sdk.
I assume rmf is a valid recipient filter class. You have to write your own class for this. Get some sample stuff here:
http://www.hl2coding.com/forums/viewtopic.php?t=31