You can not use the Online versions or the personal Desktop Software to prepare returns for clients. Intuit has 2 products for tax preparers. They are Lacerte and ProSeries. ProSeries is the least expensive. You can install ProSeries and Turbo Tax on the same computer.
Intuit (the company that makes TurboTax) has three tax software product lines for professional preparers: ProSeries, Lacerte, and ProConnect. You can find information about all three product lines at the following link. For a small number of returns you will probably find ProSeries to be the most suitable choice.
Intuit Products for Tax Professionals,
Professional Tax Preparation Software (Online & Desktop) | Intuit Accountants
And to prepare more than five e-files, you will need to sign up with the IRS as an ERO - an Electronic Returns Originator. How to become an Authorized E-file Provider…..
http://www.irs.gov/Tax-Professionals/e-File-Providers-&-Partners/Become-an-Authorized-e-file-Provide...
This answer has been verified for accuracy by an Intuit expert employee
