I have questions...
Do you want to make a custom template where the words are your own or do you want to do this all the time for any template that you might select?
If you want to do this all the time, for any template you might select, then forget about it. It would be too time consuming and tedious to be worth it, IMO. There is no automated or auto-magic way to globally change the words in every template.
However, if you want to make your own custom template or modify an existing template and use that one all the time, then it becomes substantially more manageable.
For most of them you could simply make a custom template and/or modify the HTML to change the wording to what you want. On a few though you'll find that the words are not words but really graphics (.GIF files). So, if you want to change those, you'd actually have to use PhotoShop or some such application and make your own .GIF files.
I realize this is a long winded reply...but I'm trying to give you an idea of the scope of this...
If you want more detail just let me know. I've done this before myself on a few of the Auctiva Templates...
Mike