even though the site is an asp site, it is possible that some of the supporting CSS or Javascript files may have the same name and could overwrite CSS or Javascript files from your ASP site.
Look carefully at the file structure of the power store files, and the file structure of your site to make sure that power store will not overwrite any of your files before proceeding.
If it does not look like power store will overwrite your existing site files, then it should be fine to install it to the root of your site.