IBM has published a brand new Redbook about migrating from Microsoft SQL Server to IBM Informix.

• Migrating from Microsoft SQL Server to IBM Informix

From the table of contents:

• Chapter 1. Introduction
• Chapter 2. Architecture overview
• Chapter 3. Migration methodology
• Chapter 4. SQL considerations
• Chapter 5. Database schema and data migration
• Chapter 6. Application conversion
• Chapter 7. Informix configuration and administration
• Appendix A. Terminology mapping
• Appendix B. Data types
• Appendix C. Function mapping
• Appendix D. Operator mapping
• Appendix E. Administrative and monitoring task mapping
• Appendix F. Database server utilities
• Appendix G. SQL limits

An excerpt from the preface:

In this IBM® Redbooks® publication, we discuss considerations and describe a
methodology for transitioning from Microsoft® SQL Server 2008 to IBM
Informix®. We focus on the topic areas of data, applications, and administration,
providing information about the differences in features and functionality, including
data types, data manipulation language, data definition language, and stored
procedures. Understanding the features and functionality of the two products can
assist you develop a migration plan.