You may need to look out for IP Office Technical Tip 49 which covers the effect of Windows XP Service Pack 2 on various apps - including the IMS Client.
It details some DCOM changes that have to be made. I assume that the now delayed 3.0 would have included a corrected IMS client installer.
Have pasted the text below:
Additional enhancements to the operating system, in the Windows XP Service Pack 2, are within the security of DCOM. This gives rise to applications failing to operate, without any clear indication of the failure.
Within the IP Office application range there are programs, such as the IP Office IMS client, which utilise DCOM. The following information shows how to modify the security level to enable their correct operation. When running the component services icon (from Administration) or ‘dcomcnfg’ from the command line for the first time after the service pack installation, you will receive a security alert.
Select ‘Unblock’ to continue. Navigate down to ‘My Computer’ and select properties.
Select the COM Security tab.
Now edit the limits for ‘Access Permissions’ and ‘Launch and Activation Permissions’ to allow Remote Access and remote Launch/Activation permissions for anonymous and everyone.
After changing, click OK, and close Component Services manager.