Read this Translation HOWTO entirely, especially the section on GUI translation in KDE.
Make sure you have the latest GNU gettext package installed and get as familiar as possible with it. At least have a good look at its info pages (and remember: the KDE online help provides a very convenient way to read this kind of documentation).
Take a closer look at the programs, scripts and statistical aids which will help you with translation.
Finally, make yourself familiar with CVS (if you are going to be a team coordinator) or with CVSUP (if you are just translating).
In case you've never heard so far about CVS: it's a version control system for (ASCII) files that may be changed by different users over a network. It's pretty widely in use (it is e.g. part of about any Linux distribution around). In KDE, the name "CVS" primarily refers to a server called "cvs.kde.org" where all the source code for KDE programs, the documentation, the translations and about all other things KDE are stored. To this CVS server corresponds a local client setup on your own computer which mirrors the source tree on the remote machine. This local CVS client also allows to merge team translations into the remote source tree system. -- CVSUP is an easier to use frontend that allows automated downloads of the source tree but without the ability to get something in. You won't need an extra account for it while you do need one for using CVS.
To find out how to get an account and basically all other things you may need to know about CVS take a look at The KDE Developer's HOWTO by David Sweet. As a rule, there should be only one account per translation team. But, of course, it can be more than one if your team needs them.
It won't hurt if you also take a look at the CVS Info pages. Don't panic if they should look overwhelming at first. Basically, you are going to need only a few commands and parameters: checkout (for getting something from the remote system to your local repository) and its -l parameter (for non-recursive checkouts), update (if you just want to freshen already existing stuff on your local system) and its -dP parameters (for smart directory handling), add (for telling the remote system that there will be something new), commit (to get the new stuff from your local repository to the remote source tree), remove (to delete something on the remote server) -- that's about all.
There are also some graphic frontends for CVS around that could make things a lot easier for you, such as LinCVS or Cervisia. And in case you really get interested in this subject there's now The CVS Book -- Open Source Development with CVS.