Thanks Xavier - I am trying this in my new Joomla 3 version of the site as I wanted a fully responsive site.
I have done what you have said and have "All on one page" enabled as well as the Login option, plus I have the "guest" option enabled as well.
I don't have enough knowledge to do anything with javascript but I can do a little CSS. I am finding that when I have the login part (showing on the left) and the Guest part showing on the right that it does not fit within the container of the page it is on and part of the form is flowing across onto some side modules.
The main container for the checkout process for STep 1 (which is login for my site)
<div id="hikashop_checkout_page" class="hikashop_checkout_page hikashop_checkout_page_step1"
When I use firefox inspector it shows the container in the correct position.
But the part where the Guest is showing here
<div id="hikashop_checkout_login_right_part" class="hikashop_checkout_login_right_part span8"
is the part where the form and text is flowing outside the main hikashop_checkout_page container
Its like the hikashop container page is not containing everything.
The other issue is if I view the shop on a smaller screen like an ipad or tablet, it looks even worse.
I have bootstrap setting in configuration enabled.
See photo attached of what it looks like on PC screen, ipad and iphone.
I also notice that when the bootstrap opton is set to enabled that when I get to the Australia Post shipping section, there are no radio buttons - you have to click on the header option. Is there a setting to get this back - I can't find it if there is. Customers won't know they have to click on the name "Australia Post Standard" or Australia Post Express to choose the option. Not very friendly.
And the radio buttons are missing on the payments page as well - nothing to click to select Paypal or Direct transfer thats obvious to the customer. How is this fixed?
Hope I am making sense