Hi Adrian,
Here is the way I have it going.
I have www.mysite.com - This is my site using processwire (.htaccess not set up)
Also on this site I have a folder with my sisters web site (folder theory)
Her url points at the moment to "www.mysite.com/theory"
At the moment her site works well. (thank goodness)
Is it then that when I use the .htaccess the redirection to her cannot be found i.e. "www.mysite.com/theory"
Hope this makes some sense.
Tom