If your using linux for DNS, at tht bottom of the previous link, it explains what to do in linux to your zone file(s) -look directly under the windows DNS server walkthru where it mentions BIND. However, if you need more assistance, try:
https://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/ref-guide/s1-bind-zone.html -this is for redhat- but other linux engines are very similar.
For your SPF Questions and your external DNS/ Registar needs:
If you need help creating the spf record, then go here and create one.
http://www.openspf.org/
Then you will need to copy the spf data and insert into the DNS/ Registar records as a TXT record- most likely in the same place where you have created your mx, ptr, a or c records to point your domain name to your public Nat'ed IP destination.
Now- for common sense sake-just in case someone reads this and says- 'cool Ill just slap my Ip in there and it will work!'...Remember: Dont point any record to your Private IP behind your firewall/ or on your internal network that server is physicaly on- it wont work. It needs to be the Public NAT address your web site is at ( i.e. if you Ping pinkdinos.com and it returns an IP of 65.321.45.176 - the 65.321.45.176 is the Public IP you need to point to).
Your Registar should have an option for TXT record, if you cant find it- call them and ask them where it is or if they can put it in for you.
-rjames