You may want to consider just installing wordpress yourself, manually. It's VERY easy to do and puts you in full control.
All you do is download the zip file from wordpress. Right click it (in Windows) and choose "extract all". Go to the extracted folder and inside youll see a folder called wordpress. I change that folder's name to "blog".
Inside there is a file called wp-config-sample.php... change it's name to wp-config.php, open it up and fill in your MySQL information. (Oh yeah, you need to go to your MySQL setup page in the dreamhost panel and create a MySQL database... very easy, couple of clicks, self explanatory when you see the setup page... takes about a minute). The only part (of the wp-config file) you need to fill in will be at the top and will look like this:
define('DB_NAME', 'yourdatabasesname'); // The name of the database
define('DB_USER', 'theusernameyoucreated'); // Your MySQL username
define('DB_PASSWORD', 'thepasswordyoucreated'); // ...and password
Then upload the contents of the "wordpress" or "blog" folder to wherever (the main directory of your subdomain in this case), go to that subdomain on the web and the wordpress setup will appear magically before your eyes! It will ask you for the blog's name and your email address, you press the big button and it sets it up automatically for you.
If you upload the whole folder (not just its contents) to your regular domain, then you would go to yourdomain.com/blog or yourdomain.com/wordpress to set it up, and your visitors would go to yourdomain.com/blog (or wordpress) to read it. The "wordpress" or "blog" folder itself would be the subdirectory.
This whole process can be done in about 10 minutes once you've done it one time. Ok, maybe 20 and maybe after doing it twice... your mileage may vary!