Thanks for that timeth... that link was just the job, 'though I don't know why that post never came up in my search results.
There are some nice themes there, but regarding my first question I do have this rather cool plymouth theme I downloaded (for Mandriva) called Dragon which I'd like to try to install. The readme says I need to have "plymouth-plugin-script" installed. I got Synaptic to download what seemed to be the nearest match to this but still couldn't get it to install using "-Uvh /path-to-the-download/dragon.rpm" in a terminal.
Not sure whether I'm using the right command (I'm fairly new to Linux and complete
NOOB at using the terminal!)
But the output suggested I need some other stuff... perhaps the PCLos script I used from synaptic was wrong... I don't know.