Doh! Just read your post properly

To create an htaccess file
Open notepad
Save a blank file as .htaccess (make sure you change the file type from txt to all files)
Upload the file to your server
Then in PS use the generator to re-create the file
Should be ok then
If you look at the file on the server afterwards you shoud see its not blank anymore but will have something like this in it:
# .htaccess automaticaly generated by PrestaShop e-commerce open-source solution
# http://www.prestashop.com - http://www.prestashop.com/forums
# URL rewriting module activation
RewriteEngine on
# URL rewriting rules
RewriteRule ^([a-z0-9]+)\-([a-z0-9]+)(\-[_a-zA-Z0-9-]*)/([_a-zA-Z0-9-]*)\.jpg$ /img/p/$1-$2$3.jpg [L,E]
RewriteRule ^([0-9]+)(\-[_a-zA-Z0-9-]*)/([_a-zA-Z0-9-]*)\.jpg$ /img/c/$1$2.jpg [L,E]
RewriteRule ^lang-([a-z]{2})/([a-zA-Z0-9-]*)/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$3&isolang=$1$5 [L,E]
RewriteRule ^lang-([a-z]{2})/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$2&isolang=$1$4 [L,E]
RewriteRule ^lang-([a-z]{2})/([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /category.php?id_category=$2&isolang=$1 [QSA,L,E]
RewriteRule ^([a-zA-Z0-9-]*)/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$2$4 [L,E]
RewriteRule ^([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$1$3 [L,E]
RewriteRule ^([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /category.php?id_category=$1 [QSA,L,E]
RewriteRule ^content/([0-9]+)\-([a-zA-Z0-9-]*)(.*)$ /cms.php?id_cms=$1 [QSA,L,E]
RewriteRule ^([0-9]+)__([a-zA-Z0-9-]*)(.*)$ /supplier.php?id_supplier=$1$3 [QSA,L,E]
RewriteRule ^([0-9]+)_([a-zA-Z0-9-]*)(.*)$ /manufacturer.php?id_manufacturer=$1$3 [QSA,L,E]
RewriteRule ^lang-([a-z]{2})/(.*)$ /$2?isolang=$1 [QSA,L,E]