Use Proxy to Update Windows 7

Alternatively, it is possible to configure a client running Windows 7 manually so that Windows Update can communicate with the Microsoft Update servers through the proxy. Although you can configure Internet Explorer to use a proxy through Internet Options, Windows Update cannot use these settings directly. You can configure clients running Windows 7 to determine proxy settings in two ways:

• Use Web Proxy Auto Detect (WPAD) This feature allows computer services to locate an available proxy by querying a Dynamic Host Configuration Protocol (DHCP) option or checking a Domain Name System (DNS) record.
• Use the Netsh.exe command-line tool Although Windows Update does not use the Internet Options settings directly, you can use the Netsh.exe command-line tool to import the proxy settings configured for Internet Explorer. To accomplish this goal, use the following command from an elevated command prompt:
  netsh winhttp import proxy source=ie

More Info Web Proxy Au to Detect
For more information on configuring Web Proxy Auto Detect on DNS and DHCP servers, consult the following document on Microsoft TechNet: http://technet.microsoft.com/en-us/library/cc713344.aspx.