You cannot "find the registers" because the Windows Registry is not a single text file.
It is an abstract entity that a running instance of windows creates on-the-fly, using information from many sources. One of these sources is a file in usually in
C:\windows\system32\config\sam, but this file is not easily accessible, and is encoded with an undocumented binary format.
Some tools, like chntpw mentioned by Rinzwind and Jim Salter, were able to partially figure out the binary format, and thus allow basic editing. But, as the author repeatedly says, this is not 100% reliable: the reverse-engineering is incomplete, and microsoft can change this format anytime.
Even Windows, using
regedit, can only partially manage foreign registries - you can load and unload the HKEY_LOCAL_MACHINE and HKEY_USERS hives of other registries, but not HKEY_CLASSES_ROOT.
This limitation is true for regedit.exe running under Wine as well - you can use it to load, edit, and unload HKLM and HKU from your Windows registry, but not HKCR.