EDIT:
I shouldnt have used real hostnames

The problem is that irishangling.net and durban-house.com are not resolving to the correct IP address. It seems as though they are sitting on some redirect server. os-solutions, on the other hand, is set up correctly.

More detail:

Lets say I want to know what IP address irishangling.net resolves to:
# dnsqr a irishangling.net
1 irishangling.net:
98 bytes, 1+4+0+0 records, response, noerror
query: 1 irishangling.net
answer: irishangling.net 1273 A 66.150.161.135
answer: irishangling.net 1273 A 66.150.161.136
answer: irishangling.net 1273 A 66.150.161.134
answer: irishangling.net 1273 A 66.150.161.133

(note, dnsqr is a command that comes with the djbdns package)

That IP is /not/ the 65 IP that you want it to be on. Lets try durban-house.com:

# dnsqr a durban-house.com
1 durban-house.com:
98 bytes, 1+4+0+0 records, response, noerror
query: 1 durban-house.com
answer: durban-house.com 1800 A 66.150.161.135
answer: durban-house.com 1800 A 66.150.161.133
answer: durban-house.com 1800 A 66.150.161.136
answer: durban-house.com 1800 A 66.150.161.134

Same thing. What about os-solutions.net?

# dnsqr a os-solutions.net
1 os-solutions.net:
50 bytes, 1+1+0+0 records, response, noerror
query: 1 os-solutions.net
answer: os-solutions.net 2400 A 65.248.4.86

Hey! That ones right

So what can we figure out by this? OK.. first, what in the world is 66.150.161.* ? Lets try a reverse name on it:

# dnsname 66.150.161.134
redirectf.dnsix.com

OK.. sounds like its a redirect server. Probably something set up when you registered the domains at mydomain.com.

Lets jump out of DNS and into Apache real quick.

One note you always want to keep in mind with Apache virtual hosts is that the /first/ one listed will be the one used if you type in the IP address and not the domain name. Try typing in 65.248.4.86 in your browser, and you'll get durban-house.com

OK, now that we know that.. we'll jump back to DNS and conclude this up.

Why is os-solutions.net working?
Because its resolving to the correct IP address without being redirected anywhere.

Whats going on with the other two:
You type the name in your browser. Your computer sends out a request for, say, irishangling.net. It gets to that redirect server. The redirect server then mangles the request packet. It tosses all the information about irishangling.net away and just leaves the IP address 65.248.4.86. Your browser gets to your web server at that IP address, but since theres no irishangling.net information left, it defaults to the first virutal host in apache.

Its really mixed up and confusing.. but understand whats going on?
Basically, the problem lies at mydomain.com and how they are handling your domains. All 3 of them are not pointing to your BIND server. So all your BIND information is useless. I had a friend who registered a domain at mydomain.com and we could not for the life of us figure out how to specify /my/ server for the nameservers and get rid of their stupid IP redirects.

Damn, I wasnt expecting a reply like that Thanks alot auximini, that really helps & clears a few things up for me

The only difference I can see between os-solutions.net & the other 2 domains on mydomain.com is os-solutions.net redirected to [url]http://************[url] where as the other 2 redirect to **********, ie note theres no http:// before the IP, I also noticed on the page where I set up the redirects that there was a message saying you need to include http:// before the address.
Do you think that might be the problem?? I've changed them all to redirect to http://************* now so I think I have to wait a few days to see if my changes take effect, or should this change take immediate effect?

Thanks again for your reply.

Update
Thanks to your detailed reply I posted on the mydomain.com forums to see what was up & the admin told me that I have an A record for os-solutions.net but the other 2 domains have url forwarding enabled & no A records.
I've now set A records for the other 2 domains & the changes should take effect in 24-48 hours
Thanks again for your help auximini

No problem
I still have a huge grudge against mydomain.com for not allowing you to use your own nameservers with domains you registered with them. But atleast they were helpful and its working