This is what I've tried till now:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule (.*) $1.php [L]
RewriteCond %{QUERY_STRING} ^id=([0-9]{1})$
RewriteRule ^article\.php$ /article/%1 [L]
Basically, the first set of rules converts the URLs from something.php to something.
The second set of rules is supposed to replace anything that has article.php?id=NUMBER in it into /article/NUMBER.
Apache reports:
AH00124: Request exceeded the limit of 10 internal redirects due to probable
configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary.