Debian "lenny" has the version you need: either:
(best) apt-get update; apt-get upgrade, which will query the repositories and update everything to the latest, or
(worse) update to lenny if you're running sid or etch or an earlier debian, or
(worst) download the sources and compile it yourself, although other packages using libnss3-1d could make that a headache.
You can check out the details - packages which depend on it, on which it depends, etc - at http://packages.debian.org/lenny/libnss3-1d