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The TweakGuides Tweaking Companion (TGTC) is the complete system optimization guide for Windows users. Designed for novice and advanced users alike, it is written in plain English to help you genuinely understand all aspects of Windows and your PC. The guide covers every major topic, from the correct installation of Windows and critical drivers and software, through to recommendations for every significant setting and feature, all the major performance and convenience tweaks and customizations, as well as detailed troubleshooting advice. There are also links to a range of reliable free applications for optimizing and maintaining your system, as well as to important resources for finding out even more about Windows and your PC.

For Vista: http://www.tweakguides.com/files/TGTC_Vista_1.0.zip
For XP: http://www.tweakguides.com/files/TGTC_XP_3.4.zip