hanybanoub, a "sweep" account is brokerage language which means the default cash account. In other words, if you send them a check, they deposit it in your sweep account. Similarly, if you sell stock, receive a dividend, or receive interest, then that money gets "swept" into your sweep account. It happens automatically.
Assuming that you followed the online sign-up and chose an account name and received a password, you should be able to login to your account and see your brokerage account number. One place to find it is on the "Trading" screen, which can be accessed by selecting "Trading" in the menu bar. It will appear towards the top right of that screen as a 9-digit number.
If you can't find it, then you can call their customer support at 1-800-825-5723. When I called, there were several levels of voice prompts, after which I was immediately connected to a live person who was able to answer all my questions.
I signed up online only a few days ago (and immediately mailed my check), so I should be receiving my info packet in a few days. I believe that the info packet will contain instructions for how to select which of their Money Market funds I want to use for the sweep account. A few of them currently pay between 5.4 to 5.7% interest. The customer service guy told me that until I select a Money Market fund, my cash will earn a lower rate of around 3.5% (which is better than most banks).
If you signed up through the offer link at the top of this thread, then you should be receiving your Visor within 6 to 8 weeks of funding the account. I guess if you go below $1000 in the account before the end of 6 months, then they will ding you for the $179 value of the PDA. After 6 months, simply call them and say that you'd like to close your account and receive a check for the value. Alternately, you can authorize another brokerage to transfer your holdings to them (if you have an ETrade or Schwab account, for example). If the money is invested only in a Money Market Fund, then I would be inclined to simply have them cut me a check and be done with it.