Collaborative editing of spreadsheets by multiple users simultaneously - Is it really possible?

I work in a SharePoint 2010/SharePoint Server 2010 environment and we use MS Office 2007(Excel 2007) . I have been trying to create a MS Office document which will allow multiple users to work on a spreadsheet simultaneously. For that I have:

1) Created a excel workbook and published as a workspace as suggested by Andrea Kalli in her link: http://www.wonderhowto.com/how-to-collaborate-files-between-sharepoint-and-office-2007-182172/

2) Set up and saved the Excel Workbook as "Shared" and made it available on a network share (I am assuming that the network were we use SharePoint is a "network share") so I saved the document in SharePoint.
I followed instructions to create the share workbook from "page 7 of 9" of the link: http://office.microsoft.com/en-us/excel-help/overview-of-sharing-and-collaborating-on-excel-data-HA010089896.aspx

I was hoping you could help me find out how can multiple users make changes to an excel doc uploaded to a SharePoint document workspace at the same time?

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