Re-add missing Language Support

I have in my hands a machine on which some kind of stripped-down version of
Windows XP was installed. It is missing support for Russian language (and a
few others). I believe nLite may have been used to create a custom install
CD, and many languages were stripped out.

I have original Windows XP CD, and a valid license for it. I simply
<+><+><+>MUST<+><+><+> re-enable the Russian language support without
re-installing the OS. Can I do it? How do I re-add a missing locale to XP?

Thanks very much!