Lighter roles than SYSADMIN on SQL for user creation

We are installing NAV2009 with SQL. I am the project manager and not very techy. Our external certified Navision vendor tells us that in order to use the functionality Tools > Security > Windows Login to create a new user in Navision (and in SQL) the user doing the creation needs a SYSADMIN authorisation on the SQL.

Giving SYSADMIN is against company policy and I am asked to try to find other solution. IS there a lighter profile or combination of SQL right that can be given to the user responsible for NAvision user creation and that would avoid distributing the highly powerful sysadmin rights to helpdesk people?

Thanks for you help