Vista

• that's right, you literally have to hack your own machine

XP

• checking what version of WGA is installed: go to c:\windows\system32\LegitCheckControl.dll, right-click, properties, version tab
• this registry hack worked great for me
• WGA v1.7.18.1 crack (circa March 3, 2007)
• "permanent" WGA crack (circa Dec 3, 2006)
• LegitCheckControl.dll crack (circa October 1, 2006)
• WGA .dll crack (circa August 1, 2005)
• site:mydigitallife.info wga

• directly download many of the patches (directly download ALL of them)
• viewing and changing the product key:
  • one
• keygens
  • click on "Windows XP CD Key Changer"
• disabling the "non-genuine" constant pop-up messages [1] [2]

download.microsoft.com direct-download links

• lists of links: mydigitallife.info, softwarepatch.com
• This has several suggestions, among them, just picking out the filename, and just Googling for a direct link... something like this