Found this on the msn site.....
How do I fix the error "MSN Messenger setup failed with error code '1603'" during setup?When running MSN Messenger Setup, you may encounter a "1603" error or you may get the following error message instead.
An error occurred during the installation of assembly "Microsoft.Windows.Networking.RtcDll, type="win32", version="220.127.116.11", publicKeyToken="6595b64144ccf1df", processorAchitecture="x86"". Please refer to Help and Support for more information. HRESULT: 0x80070002.
To resolve the situation:
Turn off any spyware detection programs.
If you have the Microsoft® Windows® AntiSpyware (Beta) installed, right-click the Windows AntiSpyware icon in the taskbar notification area and click "Shutdown Microsoft AntiSpyware". To turn off non-Microsoft anti-spyware programs, refer to instructions provided by the manufacturer.
Run MSN Messenger Setup again.
If this does not resolve the problem, you may not have enough free disk space. The Disk Cleanup tool calculates how to safely free up disk space on your hard disk.
To make some disk space available:
Click Start, and then click Control Panel.
Click Performance and Maintenance.
Click Free up space on your hard disk.
The Disk Cleanup dialog box appears.
On the Disk Cleanup tab, select the following check boxes:
Downloaded Program Files
Temporary Internet Files
Temporary Offline Files
Click OK to delete the files from these locations.
When prompted, click Yes start the disk cleanup.
here's the link for the most frequently asked questions page....Frequently asked questions