Is my website name legal?

[livewyre]

OK, I had a look at the site and sure enough SEONORTHSYDNEY is actually their name (note that your company name and domain don't have to be the same), so from here on in it gets tricky.
If their name was North Sydney Trading and they used the same domain (seonorthsydney.com.au), you would not have any problem, but I think because this is their actual trading name, you should be careful about it.
The separate terms 'SEO' 'NORTH' and 'SYDNEY' cannot be protected, but when you put them all together, it is unfortunate that two separate people were thinking along the same lines.
Personally I would drop this domain name and get another one - if nothing else you risk really pi$$ing off the owner of the other domain because it is going to look like a classic cyber-squat scenario even though unintended.
Hopefully you didn't pay a lot for the domain - you could even ask 'Brian' if he would like to take the domain over from you, but don't try and make a profit and fully explain that this was a genuine unintentional error on your part. Those in the game of SEO are naturally suspicious because of the nature of the business - I don't think it makes sense to go down this route. Seems to me Brian thinks a lot of himself and would not take kindly to your encroaching on his territory!
In a nut-shell...buy another domain, they are not expensive - it could save you a lot of needless hassle. Who knows, you might end up working with or for him one day..but not if he thinks you are trying to steal his business.