SQL Server '05 SP 4 Update

I have a computer - used in a business I work for - with XP OS. I am having problems installing an update for SQL Server 2005 Express Edition SP 4. I have been working with MS to try and solve the problem - but the Update Support department wants to pass me off to SQL Support. This is part of what I've been told:

Windows Update Support Professionals, we are more specialized in Windows Update issues. If you have not installed SQL Server manually, most likely, some database applications such as ACT are using SQL Server Express edition therefore SQL Server Express edition was installed by database applications. Since the installation failure of this SQL server update can be caused by corruption in the SQL program itself, we may have to recommend contacting our SQL Support team directly, who specializes in this type of issue. That being said I would like to attempt resolving this issue for you in an effort to prevent sending you to our SQL support professionals.

I followed the instructions and it still didn't seem to work. Afterwards I received an email stating in-part:

I want to confirm whether the SQL Service is used. If it is used, please try to contact SQL Support Team. If not, I suggest we can hide the update.

My question is - What IS SQL Service and do I really need it?