WP2.0 will not correctly write .htaccess for permalinks

When I update my permalinks, WP2.0 will not write the .htaccess file to reflect the necessary changes. It will write:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php
</IfModule>

# END WordPress

And no more.

I tried changing the .htacces to CHMOD 644 and updating the permalinks with hopes it would generate the right rewrite rules in the textbox and I could then manually update them, but all that appears in that box is the same as above!

As a result, comments are not viewable and indvidual posts are not viewable even if using a permalink structure beginning with index.php. I have updated functions-post.php and classes.php to no avail.

Any suggestions, need any information? Please! I have a time frame of 7 days to fix this after which I am travelling and will have very little time to correct it.

(Edit: setting the permalinks structure back to ‘Default’ makes pages visable again. I’m positive this is all to do with the Rewrite rules not being written, and I’m not sure how to do them manually (though I have tried, to no avail))