I have seen at least three instances of lovefilm's streaming service not working on windows XP. All were new installs with Service Pack 3 and all updates installed.
The issue seems to be linked to DRM. It affected all browsers. Google searches produced no useful solution. The message '"Title unavailable. Sorry, but the title is unavailable. Please try again later." would appear in some browsers.
The solution I found was to uninstall Silverlight. Completly delete the
C:\Documents and Settings\All Users\Application Data\Microsoft\PlayReady
Reinstall an earlier version of Silverlight.
The version that worked for me was Silverlight_5.0.61118.exe .
Restart the browser.
Should work OK now. YMMV but it worked for me on all three systems.
I also have it working on my HTPC now on a Virtualbox VM under linux.