Windows:

⦿ Intel Pentium 4 or AMD Athlon 64 processor (multicore processor recommended)

⦿ Microsoft Windows XP with Service Pack 2 (Service Pack 3 recommended) or Windows Vista 
⦿ Home Premium, Business, Ultimate, or Enterprise with Service Pack 1

⦿ 2 GB of RAM (4 GB or more recommended)

⦿ 30.8 GB of available hard-disk space for installation; additional free space required during 
⦿ installation (cannot install on flash-based storage devices)

⦿ 1,280 x 900 display with a 16-bit video card

⦿ DVD-ROM drive

⦿ QuickTime 7.4.5 software required for multimedia features

⦿ Broadband Internet connection required for online services

Please note that these are the minimum system requirements, and for better performance, especially when working with larger projects or more complex files, it's recommended to have a more powerful computer. 

New features:

• Photoshop CS4: Content-Aware Scaling, Vanishing Point, Refine Edge, Selective Color Correction, and more.
• Illustrator CS4: Gradient Mesh, Variable Width Strokes, Live Trace, and more.
• InDesign CS4: Live Preflight, Customizable Links Panel, Interactive Documents, and more.
• Flash CS4: Bones Tool, Tweens Applied Directly to Objects, 3D Translation and Rotation Tools, and more.
• Dreamweaver CS4: Live View, CSS Gradients, Spry Widgets, and more.
• Fireworks CS4: Slices Panel, CSS Export, and more.
• Contribute CS4: Conditional Content, Snippets, and more.
• After Effects CS4: Autofill Searches for Timelines and Projects, Improved Round Tripping Between Applications, and more.
• Premiere Pro CS4: Speech Search, Improved Collaboration Tools, and more.
• Soundbooth CS4: Speech Search, Improved Collaboration Tools, and more.
• OnLocation CS4: Improved Editing Tools, New Effects, and more.
• Encore CS4: Improved Blu-ray Support, New Output Options, and more.
• Bridge CS4: Improved Resource Management Tools, and more.
• Device Central CS4: More Extensive Device Selection, Improved Simulation Options, and more.
• Version Cue CS4: Improved Collaboration Tools, and more.

In addition to these new features, CS4 also included a number of workflow improvements and bug fixes.