htaccess redirect to subfolder with exception - wordpress

Question

I've searched quite a lot without finding a solution.
I have a wordpress blog in /_wp and something else in /other
What I'm trying to is that every request gets redirected to the WordPress. Except those to /other and its child directories. I also want the access to the blog to be rewritten. Few examples to make it clear:
/ --> /_wp/
/ablogpost --> /_wp/ablogpost
/other --> /other
/other/bingou --> /other/bingou
I've tried a few things but what seems the most logical to me is:
don't touch the .htaccess of /_wp/ and of /other/
edit the .htaccess of the root '/' by adding:
RewriteEngine on
RewriteCond %{HTTP_HOST} ^(www.)?mywebsite.com$
RewriteCond %{REQUEST_URI} !^(/other|/other/.*)$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^/?(.*)$ /_wp/$1
If you could tell me what is wrong there it would be great!
EDIT
After changing the index the subfolders were still not working here was my .htaccess back then:
IndexIgnore .htaccess */.??* *~ *# */HEADER* */README* */_vti*
<Limit GET POST>
order deny,allow
deny from all
allow from all
</Limit>
<Limit PUT DELETE>
order deny,allow
deny from all
</Limit>
AuthName site.com
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
EDIT 2
In the end it was a host problem thanks for your help though! Your answer works just well

Answer 1

You should follow this : http://codex.wordpress.org/Giving_WordPress_Its_Own_Directory
Your wordpress install is already in its own directory, so you just have to :
Copy /_wp/.htaccess to /.htaccess
Copy /_wp/index.php to /index.php
Edit /index.php :
require('./_wp/wp-blog-header.php');
Edit /.htaccess
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]