Actually there is not such version as "multiple users" or anything of the such with the program.
If you are using the CD/Desktop version of the program that you physically install on your computer, you can use it to complete as many tax returns as you want.
If you are using the online version of the program, then you can only do one tax return per online account. Period. But you can create up to 5 accounts per-email address. So with the online version, one account, one return. It's also considerably more expensive to use the online version if you need to complete more than one tax return.
