CRM 4 web client won't connect

Hi

I've set up CRM 4.0 as a new install on a new install of SBS 2008 and I can't connect to it from any other computers through the web client. I haven't tried the Outlook client yet as I'm presuming the same problem will occur. Here's some details on what I've tried so far:
On the client I try http://crm and I get
This problem can be caused by a variety of issues, including:

"Internet connectivity has been lost.
"The website is temporarily unavailable.
"The Domain Name Server (DNS) is not reachable.
"The Domain Name Server (DNS) does not have a listing for the website's domain.
"There might be a typing error in the address.
"If this is an HTTPS (secure) address, click Tools, click Internet Options, click Advanced, and check to be sure the SSL and TLS protocols are enabled under the security section.

http://servername:5555 gives me the same result.
I've tried this on a Windows 7 client and also one running XP
On the server I can browse to http://servername:5555 but not to  http://crm

The users I'm trying to log on from are set up as CRM users.

I appreciate any advice you can give

Mick