loadable kernel modules

[giamma]

Hi, i'm a newbie for FreeBSD and I've just installed the 5.0 on my box. Here 
is the problem: I've an internal modem on COM3, and after running sysinstall 
I've discovered that i've only 2 serial ports (cuaa0 and cuua1) corresponding 
to COM1 and COM2. How can I do to set up a new serial port on COM3?
I must rebuild my kernel? Or edit /etc/rc.serial? Or i have to use mknod?
Thanks in advance for your help!!! 
Greetings, Gianmario Tamagnone.