ACT! 2011 Minimum
System Requirements

Microsoft® Windows® XP Home (Service Pack 3), XP Professional (Service Pack 3), Windows XP Media Center (Service Pack 3), any Server 2003 (including Small Business Server 2003) with Service Pack 3, Microsoft Windows Vista™ Home Basic, Vista Home Premium, Vista Business, Vista Ultimate, Vista Enterprise. Note: You cannot install on a workstation or server that is using Windows 2000 or Windows NT.
Minimum 1.8 GHz Pentium IV
Minimum 1GB RAM 2GB strongly recommended
Minimum 2GB of available hard disk space
CD-ROM drive
SVGA (800x600) or higher resolution monitor

Using Microsoft SQL ServerTM 2008 Express Edition [EX]: Microsoft Windows XP Home (Service Pack 3), XP Professional (Service Pack 3), Windows XP Media Center (Service Pack 3), Any Server 2003 (including Small Business Server 2003) with Service Pack 3, Microsoft Windows Vista Home Basic, Vista Home Premium, Vista Business, Vista Ultimate, Vista Enterprise.
Using Microsoft SQL Server 2008 Standard Edition [ST]: Any Any Server 2003 (including Small Business Server 2003) with Service Pack 3, Microsoft Vista Enterprise.
1GB RAM; 2GB+ recommended
Minimum 2GB of available hard disk space

Note: Windows XP, Vista Business, Vista Enterprise, and Vista Ultimate editions limit the number of concurrent users to 10.

ACT! 2011 Works With:

Microsoft Outlook® 2003/2007/2010 Note: It does NOT work with Outlook 2000 or 2002/XP
Microsoft Outlook Express 5.5/6.0.
Lotus Notes® 6.5. If installed on Windows Vista, Lotus Notes 7.02
Eudora® 5.2/6.0
Microsoft Office 2003/2007/2010 Note: It does NOT work with Office 2000 or 2002/XP
VMware Workstation 5.0/5.5 and VMware Server 1.0.1