To connect via USB and access mass storage mode:
Go into settings, Wireless & Network, USB utilities, USB mass storage and tap the "connect storage to PC" button, then connect to PC and follow the prompt.
If you don't want MTP mode, don't just connect to PC first unless USB debugging is turned on. When it is turned on, connect up, then follow the prompts from the status bar pull down.
If I connect mine with debugging turned off, the phone goes to MTP mode, PC sees it and I can access, but it doesn't show .hidden folders or files.
3 ways to get into it.
I'm pretty sure Kies was able to work with the device just in MTP mode when I did my 2.3.6 update via USB connection.
There is a "usbStorage" folder within the device internal memory. It's not actually separate internal storage. I found to root my phone with recovery mode, I had to place the zip files in there for it to work. Putting them in the "external_sd" folder in the device memory failed. This folder is not your external card, that appears separate under Windows Explorer.
Confusing compared to my old phone, but I got used to it.