Can I start a SMPT server on slackware 10.2 ?

do you mean an smtp server like sendmail?

Yes..

in the /etc/rc.d folder there is a file called
rc.sendmail
make that file executible and it will load at boot
you can also type
./rc.sendmail start|stop|restart
depending on what you want to do

and the adress of this server is my IP no? what about the username and password ?

yes the address will be the IP of the slackware machine.
i would recommend downloading www.webmin.com and use that interface to configure sendmail.
it isn't as simple as turning it on and go.

By default, there is no requirement for username/password to send an email. Once you have set the /etc/rc.d/rc.sendmail to executable (chmod a+x /etc/rc.d/rc.sendmail) and or ran it manually (/etc/rc.d/rc.sendmail start) it should automatically begin accepting connections.
You would set your SMTP server to the ip address of your box, for example, 192.168.1.25
You really should set specific rules in the /etc/mail folder in the access files etc. so that people wont relay tonnes of spam off of you, there are plenty of good howto's on this everywhere as it is a pretty big problem.

Do you have two NIC's? Are you using 2 IP addresses (one internal, one external), do you want it to just send mail from the localhost (ie only from you sending from that specific mail server)

can i configure me slackware machine to run a SMTP server without user name or password ? because I don't need very much user name and password just to put de IP of me slackware machine ? works ?

Yes.

if I'n not apear to stupid but I'm a newbie ... where is the line in /etc/rc.d/rc.sendmail ho starts the SMTP ?

type the following to enable and start sendmail:

cd /etc/rc.d/rc.sendmail
chmod a+x rc.sendmail
./rc.sendmail start

and I anderstand that me SMTP works now ? without user name and password just de IP of me slackware machine ???

Sendmail is called an MTA, something that handles SMTP requests on your machine.
The purpose of rc.sendmail is to start, stop or restart your SMTP services
.
If you type in ls -l /etc/rc.d/rc.sendmail you should get an output like this;
-rwxr-xr-x 1 root root 687 2002-06-04 14:09 /etc/rc.d/rc.sendmail*

if it says -rw-r--r-- instead of -rwxr-xr-x then you need to type...
chmod a+x /etc/rc.d/rc.sendmail
and then
/etc/rc.d/rc.sendmail start

And you are all set to send messages though your slackware box.

Haha, looks like we are all posting at the same time ;-)

thx for all the help