If your are trying to make them run independent from each other, your suggestion should work fine. (Assuming you mean “www.mysdrupalsite.com/wordpress/”.) Just make sure you create a separate database for this new wordpress installation. If you have only one database and it is already in use, you can install WordPress in it – just make sure to have a distinctive prefix for your tables, to avoid over-writing any existing database table.
Combining the two in one (for example users can use both, only singing up once) will be much tougher. If your looking for this, please let me know and I can explain it for you.
More/all indept information on how to install wordpress can be found here.