Windows 7 is not required to run Project Professional 2010. From http://technet.microsoft.com/en-us/library/ee624351.aspx#section12, the OS requirements for Project Professional 2010 are: Windows XP with Service Pack (SP) 3 (32-bit), Windows Vista with SP1, Windows Server 2003 R2 with MSXML 6.0, Windows Server 2008 or later (32-bit or 64-bit), Windows 7 or later operating systems.
For the browser-only users using the Project Web App in SharePoint 2010, Microsoft Internet Explorer 7 or Microsoft Internet Explorer 8 is required; see http://technet.microsoft.com/en-us/library/ee683978.aspx#section8. Although SharePoint 2010 does have some support for non-Microsoft browsers, Project Server 2010 does not.
