Hi chrisdonals1,

After reinstalling the Operating system, there is a certain order in which the drivers have to be installed.

The following article (Article ID: 268873) describes how to download and install drivers in the correct order:
http://support.dell.com/support/topics/global.aspx/support/kcs/document?c=us&docid=268873&doclang=en&l=en&s=gen&cs=

Answering your questions,

• Yes, you are correct INTEL_825XX-GIGABIT-PLATFORM_A06_R290983 is the correct driver for Ethernet Controller.
• Following link is for the Chipset driver:
  http://www.dell.com/support/drivers/us/en/19/DriverDetails/Product/optiplex-980?DriverId=R302424&FileId=2731118163&DriverName=Intel%20Chipset%20Software%20Installation%20Utility%2C%20v.9.2.0.1030%2C%20A05&urlProductCode=False
• Intel_AMT-HECI_A05_R304259 is for Host Embedded Controller Interface (HECI), and it needs to be installed too.
• Dell Support Center has the feature which identifies the driver updates for the computer. Use the link provided below, select your region and follow the on-screen instructions to install Dell Support Center: http://www.dell.com/dellsupportcenter

Drivers needed to be installed in the computer can be found at our support website. Follow the below mentioned steps to locate the exact drivers compatible with your computer:

• Visit http://www.support.dell.com
• Click “Start Here” under “Support for Home Users”.
• Click “Drivers & Downloads” icon.
• In the next page, enter the “Service Tag” of the system in the box provided and click “Submit”.
• In the next page, under “Refine your results”, click drop down arrow for choosing the Operating System and click “Windows 7 32-bit”.
• Page will display all the Drivers & Applications which are to be installed for your computer.

Please post with the results.