I copied the details of SQL Server 2005 SP3 from the link below, It describe the system requirements, steps, which edition of sql server that applies with this version of service pack.
Service Pack 3 for Microsoft SQL Server 2005 is now available. SQL Server 2005 service packs are cumulative, and this service pack upgrades all service levels of SQL Server 2005 to SP3. You can use these packages to upgrade any of the following SQL Server 2005 editions:
Note: To upgrade SQL Server 2005 Express Edition, obtain the SP3 version of Express Edition or Express Edition with Advanced Services.
For a list of new features and improvements that are included in SQL Server 2005 SP3, review the What’s New document.
Top of pageSystem Requirements
•Supported Operating Systems:Windows 2000 Service Pack 4;Windows 7;Windows Server 2003;Windows Server 2008;Windows Server 2008 R2;Windows Vista;Windows XP
•32-bit systems (x86)
◦PC with Intel or compatible Pentium III 600 MHz or higher processor (1 GHz or faster recommended)
•64-bit systems (x64, ia64)
◦1GHz or faster processor
•Minimum of 512 MB of RAM (1 GB or more recommended)
•675 MB of available hard disk space
Note: SQL Server 2005 Service Pack 3 (SP3) is designed to run on Windows Vista and Windows Server 2008. For more information about installing and running SQL Server 2005 on Windows Vista and Windows Server 2008, see this Microsoft Web site.
Top of pageInstructions
Note: You must have administrative rights on the computer to install SQL Server 2005 SP3.
Step 1: Download and review the setup documentation and readme file. For known issues, review the release notes.
Step 2: Download the appropriate package by clicking one of the links below. To start the installation immediately, click Run. To install SP3 at a later time, click Save.