Hi James,
Assuming you want to keep the existing setup but set up friendlier URLs (example, redirect ?p=1_14 to /p/1_14), you could do something like this:
RewriteCond %{REQUEST_URI} ^p=([^&]+) [NC,OR]
RewriteCond %{REQUEST_URI} &p=([^&]+) [NC]
RewriteRule .* /p/%1? [R=301,L,NE]
Then you'd want something to handle those new URL requests with something like this:
RewriteRule "^p/(.*)$" "/index.php?p=$1" [L,NE]
Hope this helps!