QuickBooks Pro 2009 has the ability to open a company in Multi-User Mode, allowing more than one person to work at the same time.

To open a company file in multi-user mode follow these steps:

1. Go the the File menu and click Open or Restore Company

2. Select Open a company (.QBW) and click Next

3. In the Open a Company window, select Open in multi-user mode and then select the file you wnat to open.  If you accidentally open the file in single-user mode, you can switch to multi-user mode by following these steps:

1. Go to the File menu and click Switch to Multi-User Mode.

2 If there are other people waiting to work with the company file, tell them they can log in.

The above information is provided by http://support.quickbooks.intuit.com