You didn't mention your OS, but for Windows Vista/7 you can paste the following code into Notepad and save it as Take Ownership.reg (or whatever). Run it, and an option named Take Ownership will then appear in the contest menu when you right-click a file or folder. If selected for a folder, the folder and all subfolders will be processed - make take minutes - and the user account from which this is done will be the owner, and therefore have access to the file(s)/folder(s) selected. In theory. I have found that sometimes some subfolders are apparently not processed, and must then be processed separately, which is simple enough.
Code begins below:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\*\shell\runas]
@="Take Ownership"
"NoWorkingDirectory"=""
[HKEY_CLASSES_ROOT\*\shell\runas\command]
@="cmd.exe /c takeown /f \"%1\" && icacls \"%1\" /grant administrators:F"
"IsolatedCommand"="cmd.exe /c takeown /f \"%1\" && icacls \"%1\" /grant administrators:F"
[HKEY_CLASSES_ROOT\Directory\shell\runas]
@="Take Ownership"
"NoWorkingDirectory"=""
[HKEY_CLASSES_ROOT\Directory\shell\runas\command]
@="cmd.exe /c takeown /f \"%1\" /r /d y && icacls \"%1\" /grant administrators:F /t"
"IsolatedCommand"="cmd.exe /c takeown /f \"%1\" /r /d y && icacls \"%1\" /grant administrators:F /t"
Code ends above.