Mandriva will struggle on a PII 400 with 128 Mb RAM; I'd go for Suse 9.1 or 9.2 if available. (I've got them on CD if you want).
It's fairly straightforward to install both Mandriva and Suse. When you connect a USB printer they will both install it pretty simply.
When installing either, do a custom install and install just the bare minimum; you can then install a word processor afterwards.