PC Games Hardware has word from Ubisoft that no demo is planned for the upcoming Venice add-on for Anno 1404, the strategy sequel also known as Dawn of Discovery. They also have the system specifications for the expansion:

The Minimal system requirements of Anno 1404 Venice:

• Processor: 3 GHz Intel Pentium 4 or comparable
• RAM: 1 GiByte
• Graphics card: 128 MiByte video memory with Pixel Shader 2.0

The Recommended system requirements of Anno 1404 Venice:

• Processor: Intel Core 2 Duo E4600 (2.4 GHz) or AMD Athlon 64 X2 4800+ (2.5 GHZ)
• RAM: 2 GiByte
• Graphics card: 512 MiByte video memory with Pixel Shader 3.0