There are a number of good pages which explain how to enable permalinks and rewrite rules for WordPress, such as:

http://codex.wordpress.org/Using_Permalinks
and
http://faq.wordpress.net/view.php?p=20

None of them mentioned my problem – the main apache conf for the website had the setting AllowOverride None.

Hence my .htaccess wasn’t being honoured, hence my redirects weren’t working (and resulted in 404’s). Hence i ripped a clump of my hair out.

gah. hopefully someone stumbles across this and doesn’t waste as much time as i did.