I have had a ps3 for a while and have always had an issue where my ps3 would disconnect with a DNS error 80710102, however it would only disconnect after around 3 hours so it was never a huge issue. I just went out and bought Killzone 2, and when trying to update the software it has never made it to 20% updated without disconnecting, and making me start over. I have tried for around 2 hours and can't get it to work. I have manually entered the IP address and the DNS address, the SSID and the security code, nothing is working.
Any ideas how to get this thing up and running?

First, I doubt it's a "DNS" issue that's disconnecting you. Once the system makes the DNS request and finds the servers IP address it doesn't need to make another during the transfer.
What it actually sounds like is that your router is having NAT issues. I'd look into the settings on your DSL/Cable Modem/Router and see if you can do static port forwarding. At that point, assuming you can you'll want to check out Sony's help forums and request the ports that the PS3 and specifically the Killzone Update uses. Once you have those, you'll set a static IP for the PS3 server, and forward those ports to that IP.
If it's still dropping you, the next step to look at is a firewall you have running. Your router/modem probably has a basic firewall in it, and you may need to allow access from Sony's servers. If the update takes a while it may lose it's TCP session and the reestablishment of such may be causing the firewall issues, so we're going to allow inbound from those IP's that are needed.
If none of those work, let me know and I'll throw some more ideas your way.

Since you mention having an ssid, my first thought would be to look for wireless interference. Shifting to a different transmission channel on the router might help
If port forwarding was an issue it should be consistent and near immediate so I'd discount that as a primary cause (not impossible but it'd be a very odd error)
Download InSSIDer and run a scan to see how many other wireless signals are in the area and see if they're on a close channel to yours.
Weird question but would a microwave be running when you're having these problems? I know one guy who gets wireless dropouts whenever his microwave is on, presumably it spikes in the 2.4ghz band

I believe I have found the issue. The PS3 was set to constantly search for media signals, which interfeared with the wireless connection. This sent me a generic DNS error report and disconnected me. The reason I suspect this is because after messing with he settings I disabled the Media Search and it is working now.
The proper ports are already opened (tried that before). The error number actually specifically says that the connection is being dropped due to an unstable connection.

The reason I mentioned port forwarding is because I'm guessing that it uses a range, and if it's hopping ports the auto negotiation may be failing with the router.
As for the microwave, it's a known issue, but it only happens with unshielded, or damaged microwaves. He should either get the appliance fixed or replaced.

Pretty sure that the PSN uses 3-4 static ports, I set it up once but since I don't own one I've not paid much attention since.
Hehe yeah I've told him to get a new microwave but his 'safety conscious' / lasy arse reply is words to the effect of "Meh, I just won't use the net when cooking"

Oh well, maybe the microwave will sterilize him and the gene pool will be better off in the end. ;)

Well if they microwave can't do the job, I've got a rusty blunt stanley knife...

nevermind this post, what I said didn't make too much sense.

I managed to move the topic of this thread from DNS problems to neutering my friend with a blunt knife. I don't think you making no sense is an issue

Too late! I already saw what you wrote! Now I'll know your secret forever!!