PeopleSoft is certified on SQL Server 2005 (32 bit, x64 and Itanium). The following comprehensive whitepaper written with Oracle and SQL Server Product Team is a great resource for PeopleSoft Customers.
Microsoft SQL Server 2005 Tuning Tips for PeopleSoft 8.x
This white paper is a practical guide for database administrators and programmers who implement, maintain, or develop PeopleSoft® applications. It outlines guidelines for improving the performance of PeopleSoft applications running on Microsoft® SQL Server™ 2005.
Much of the information presented in this document is based on findings from real-world customer deployments and from PeopleSoft benchmark testing. The issues discussed in this document represent problems that prove to be the most common or troublesome for PeopleSoft customers.