ACT! Minimum
System Requirements

Microsoft® Windows® XP Home (Service Pack 2), XP Professional (Service Pack 2), Windows XP Media Center (Service Pack 2), Server 2003 Standard Edition, Server 2003 Enterprise Edition, Server 2003 Web Edition, 2003 Small Business Server operating systems (all Server 2003 need Service Pack 2), Microsoft Windows VistaTM Home Basic, Vista Home Premium, Vista Business, Vista Ultimate, Vista Enterprise.
Minimum 600 MHz Pentium III (or equivalent) processor
Minimum 512 MB RAM
Minimum on Vista and Recommended on XP: 1.8 GHz Pentium IV (or equivalent) processor
Minimum on Vista and Recommended on XP: 1 GB RAM
Minimum 1GB of available hard disk space
CD-ROM drive
SVGA (800x600) or higher resolution monitor

Using Microsoft SQL ServerTM 2005 Express Edition: Microsoft Windows XP Home (Service Pack 2), XP Professional (Service Pack 2), Windows XP Media Center (Service Pack 2), Server 2003 Standard Edition, Server 2003 Enterprise Edition, Server 2003 Web Edition, 2003 Small Business Server operating systems (all Server 2003 need Service Pack 2), Microsoft® Windows® Vista Home Basic, Vista Home Premium, Vista Business, Vista Ultimate, Vista Enterprise.
Using Microsoft SQL Server 2005 Standard Edition: Server 2003 Standard Edition, Server 2003 Enterprise Edition, 2003 Small Business Server operating systems Enterprise Edition, 2003 Small Business Server operating systems (all Server 2003 need Service Pack 2), Microsoft® Windows® Vista Home Basic, Vista Home Premium, Vista Business, Vista Ultimate, Vista Enterprise.

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