I have 2 nameservers (prim & sec) set up and working fine, lets call them ns0.example.com and ns0.example.net. They were was hosted at ISP1, and I'm moving to ISP2. The registrar was originally ISP1 but is now completely separate from them both. I've moved all the other domains originally hosted and pointed to from ISP1 to ISP2 (www.myfoo.com, www.mybar.com ..) and set their nameservers to be example.com. All that works great. What I now need to do is move example.com and example.net itself away to ISP2. How can this work? Won't I be telling the registrar of example.com that example.com's nameserver is example.com and create an unresolvable loop?
I'm ok hand editting the zone files, is this what NS recs are for? Any example greatly appreciated, thanks.

Nope. You will tell your registar that the primary dns of example.com is ns0.example.com (i.e. the FQDN) with IP xx.xx.xx.xx and secondary dns ns1.example.com - IP yy.yy.yy.yy and the same for example.net. There is no loop because when somebody looks up your domain example.com the root servers will forward the query to the dns authoritative for example.com which is ns0.example.com. Then your dns reads the zone file for the domain example.com and gives the answer. There is nothing special in the zone file to worry about but in any case here is an example.

Regards