running two or more instances on same machine...
Ex. 1 server and one o more clients on same machine, the dplay_id will be the same...

corretly?

Check out this article & code: http://opserver.de/nwik5/index.php?title=Multiplayer

The Server will manage the ids and send them to the clients...
It will start with 0 as usual for the server and 1+ for the clients.
Server: 0 <- started a new empty server
Client: 1 <- a client connected
Client: 2 <- a second client connected
...

Not very hard, IDK wheres your actual problem.
I would also suggest to use ANet, I simply love it

That's not how dplay_id works, though. (It seems to use the server's system time instead or something like that.)

I´m understanding
I can show the dplay_id corretly in the screen with:
var test

main loop....
draw_text(str_printf(NULL,"bps: %.0f",(double)dplay_id),20,40,COLOR_WHITE);

But, I can´t get put this inside a variable... ;(

What the hell are you doing xD
Its simply a var no double or float <_<