All of these programs are for changing windows configuration or content. Please make sure you know what you're doing with them. All programs are free.
FreshUI:
A nice program for changing basic windows configuration. It includes the ability to make windows stop saving information of what programs or documents you have used, and when.Resource Hack:
A great program for changing some of the hidden windows stuff. You will have to Google it to get it.Theme Manager:
With this, you can change the look of windows, and a variety of other common programs, like WinAmp and some ICQ clients.Microsoft Powertoys:
A series of small applications, witch can add small, but cool features to windows. They are made by the developers of windows, but are released separately.Regedit:
The built-in windows registration editor. Be really careful with this, as it can mess thing up really bad.
To open, just type "regedit" in the Run option from the start menu.Gpedit:
Also a built-in windows program. This is mostly used for changing template information and such stuff. Type "gpedit.msc" in Run, to open.