To stop messenger from loading when visiting sited such as hotmail delete the following key. But remember to backup your registry before doing anything to it. This works in Windows 2000 also.
1. Start > run > type regedit
2. Navigate to the following key
3. This can be done easily by searching for F3A614DC in the registry and it will automatically take you there.
4. Delete this key and you will see that messenger does not load anymore when visiting hotmail. Happy tweaking.