Not sure if you are looking to clean up that existing site or if you are looking to start with fresh download but look at some of the posts here in the forums in regards to "Spam"

Also, topic  Moved.

I ran into a similar problem when working on someone's site.  Basically, he had left his site unattended for a few months and it quickly became overrun with spammers.  It was so bad that there was a new blog post every minute, and this was causing his site to stop responding as a result.

I moved the site into another directory, which kept the spammers away long enough to fix the damage.  Basically, deleting several thousand profiles from the database and reinstalling the blogs module.  The forums were also overrun with spam posts, but there were some topics he wanted to keep, so I had to remove some thousand entries from the forum's database tables.

It wasn't fun, but within an hour, everything was back to normal.  Oh, and for the spammers, I used this little fix: http://www.boonex.com/forums/topic/How-To-Block-The-Entire-Planet-From-Joining-Your-Site-well-almost.htm

There hasn't been a single spammer since.