I don't have an sipgate account, but you can try this configuration:
In express talk's Line Options,
- Set "Full 'Friendly' Display Name" to anything of your choosing
- Set "Server (SIP Proxy or Virtual PBX)" to sipgate.co.uk
- Set "SIP Number (or User Name)" to Your SIPID (You can find it under 'My Data' / Connection information at sipgate)
- Set "Password" to your sipgate password (You can find it under 'My Data' / SIP-Password at sipgate)
Click ok to apply the settings. Within the next few seconds, Express talk's log at the bottom of the window should either indicate the account was successfully registered or give an error if there was a problem.