General :: Services Work Nicely With Connection Tracking - Port Range For Centos?

On my CentOS 5.4 box I run dns, ssh, and smtp servers. This box also has to be able to resolve and browse websites. So basically it needs iptable rules for

TCP 22 25 80 443
UDP 53

My question is, which of these services work nicely with connection tracking? I'm a little confused about how connection tracking works. For example say this iptables rule for smtp

Code:
iptables -A INPUT -s 0/0 --sport 513:65535 -d $myip --dport 25 -j ACCEPT
versus

Code:
iptables -A INPUT -s 0/0 --sport 513:65535 -d $myip --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT
So with connection tracking what exactly does it do that my first iptables rule does not do?

Also for centos is that port range correct? 2.6 Linux kernel randomly chooses a port 513-65535 when it connects to an external smtp server or say browses a site.