When you say "installer" can you be more specific about what "installer" you used and the steps you took,
And what platform you were running this install on.

We have literally hundreds of different applications and web platforms all running on the same server - co-existing quite happily - it just comes down to how you set things up.

In reality - these are the steps we use any time we install DNN
- create a folder on your server, unzip the latest install.zip version of dnn into this folder
- set permissions for this folder so that NETWORK SERVICE has full access,
- start MS-SQL Manager and create a new database - create a database user with password - assign user full access to database
- open IIS - create a new website pointed to the folder you setup earlier
- define a domain for this new website  -  mydnntest.local
- either in HOSTS file or your local DNS manager configure mydnntest.local to point to your server
- open application pool and make sure NETWORK SERVICE is set as User Identity for the application pool associated with the new website.
On your web browser - browse to mydnntest.local - and follow the installation wizard steps.

Following these steps there is no way that any other application hosted on your web server could be effected.

Westa