Traditional DNS Howto - NS record question

[showe1966]

Hi,
First all apologies for the dumb question- i know not a lot about mail servers and DNS.
I have just one computer to assign a dns to.
I read all about how I should have a backup name server in case the primary server goes down.
So, what do I write in my zones file if I only have one server ?
And, is it okay fro me to host my mail server using an mx record at the same ip address.
my zones file currently looks like this.
I think that the second NS entry is redundant but i don't know:-

@ IN SOA server1.mydomain.com. root.localhost. (
2007010205 ; serial, todays date + todays serial #
28800 ; refresh, seconds
7200 ; retry, seconds
604800 ; expire, seconds
86400 ) ; minimum, seconds
;
NS server1.mydomain.com. ; Inet Address of name server 1
NS ns0.mydomain.com. ; Inet Address of name server 2
;

MX 10 server1.mydomain.com.;
MX 20 mail.anotherdomain.com.;
;
mydomain.com. A 88.456.123.46
www A 88.456.123.46

server1 A 88.456.123.46
ns0 A 88.456.123.46

ftp CNAME www.