OK, thanks for the clarification. Unfortunately, I always think of too many oddball possibilities. ;-)
There are many ways to do what you want. You can do it:
At the command line using the REN command.
http://www.computerhope.com/renamehl.htm
http://technet.microsoft.com/en-us/library/bb490987.aspx
Using Windows file explorer.
http://support.microsoft.com/kb/320167 (for XP)
http://lifehacker.com/5826412/to-quickly-rename-multiple-files-in-windows-just-hit-tab-or-f2 (for Win 7)
Using Bridge.
http://blogs.adobe.com/educationleaders/2007/09/batch_renaming_photographs_usi.html
Using Lightroom.
http://blogs.adobe.com/jkost/2011/03/lr-3-renaming-files.html
Using plug-ins for Lightroom.
http://www.robcole.com/Rob/ProductsAndServices/FileRenamerLrPlugin/
Using specialized bulk renaming standalone programs, many of which are free. Personally, I would recommend this approach. eg,
http://www.bulkrenameutility.co.uk/Main_Intro.php (one that I use)
http://www.techsupportalert.com/best-free-rename-utility.htm (big list)
However, no matter which method you use, I have a few suggestions.
1) First, and most importantly, before you do anything, make a backup of all the files that you intend to rename, and then put these backup files in a completely different, essentially untouchable, safe location. This way, if the file renaming process goes bad, it will take you only seconds to get back to where you started. This is critically important because there are so many ways a bulk file renaming operation can go wrong, and you can easily be left with a mess of files with very, very odd file names that are nearly impossible restore to their original names unless you do it manually.
One of the major reasons for mentioning methods (ie, Bridge, LR, LR-plugins, utility programs) that show you exactly what the new names will be before the changes are actually made is to avoid the problem mentioned in the previous paragraph.
2) My second suggestion is to leave the original file name and number at the start of the new file name and number. Then append whatever new information you want after the original file name.
There are many reasons for this, for example, this way you are essentially ensured of having a unique identifier in every filename, and that ID number is always in the same position. This makes it easy to find related versions of the same file.
3) I reserved my third suggestion for last because it does not, strictly speaking, answer your question. Instead, I would suggest a completely different approach. My third suggestion is that before you embark on any mass renaming project, you should get & read through a copy of a book called," The DAM Book":
http://thedambook.com/
http://www.amazon.com/dp/0596523572
The reason is that you are reinventing the wheel. Many, many people before you have faced the exact same problem you are facing. The conclusion of many, if not most of these people is that systems like the one you are considering may work for relatively small numbers of files, but once you get into the thousands of files, systems like yours almost always become unwieldy, prone to naming conflicts, difficult to remember exactly how you named something, etc.. For example, will you remember if you named the nice photo of your wife on vacation a couple of years ago under "vacations", "portraits", "family", "Grand Canyon", or something else.
Much better methods exist, and it's vastly preferable for you to seriously consider these approaches before you embark on such a project, rather than being forced to change your archive system after you have several thousand images in your photo archive and need to rename all of them, add keywords, etc.
HTH,
TJM
PS - FWIW, I use the methods suggested in the DAM book. I have well over 250,000 images in my photo archive and can usually find any individual one of them in a matter of seconds, and all the variants of it (eg, other sizes, B&W, etc.) in another few seconds.
