Safari can’t connect to the server

I have trolled internet high and low regarding this issue I'm having ...I'm just about loosing it now. Hope somebody can help....here we go.
System spec:
Macbook pro > OS X Snow leopard version 10.6.7 > Safari version 5.0.5
Broadband supplier : Sky
I get following error message when accessing certain websites
"Safari can’t connect to the server."
May I add it's indiscriminate of which browser you use (e.g. firefox, chrome)
This issue has been going on for couple of weeks now.
Example of some websites are amazon.co.uk, apple.com (ironic), twitter.com etc.
Please note that I can access those website fine using my iphone, so it rules out the ISP.
And also, my Macbook pro connects to those websites fine at work. Bizzarre, bizzarre, bizzarre.
If anybody would be so kind to help and restore my sanity, I should extremely be grateful.

It may sound over simplistic, but it would seem the problem is with your ISP. If you can access those sites using the same MBP from your office but not at home, that kind of narrows it down.

And since your iPhone is working OK, it might be a local DNS problem with your ISP.

Sorry to sound thick but my IPhone is also using the same (sky) ADSL connection via the home wireless router. If there was issue with the local DNS, shouldn't the iphone have the same issue with not being able to resolve the URLs as my Macbook Pro?
Thank u for replying.

You would think so. However, based on my own experience that may not be necessarily true. My Mac here at home had a similar difficulty while my PC also here at home had no difficulty at all. I changed my DNS settings for the Mac to "OpenDNS" and the problem went away. I'm not saying that will work for you, but it might be worth a try.

Thank you so much for getting back to me.
I have tried OpenDNS.
Under the DNS servers
208.67.222.222
208.67.220.220
And under the DNS search it says
Home

Despite those entries I still can't access amazon.co.uk and twitter.com ( weirdly enough I can still connect to amazon.com not amzon.co.uk)

Another update...
With the OpenDNS i can connect to apple.com (can't connect to amazon.co.uk & twitter though)
But without the OpenDNS i can't connect to apple.com.