My first ever 7km Sun Run. 1 week to go, how to prepare?

Appleness

So I've begun 2013 in a good way. Going to the gym in my lunch break every day doing classes and when i can doing a 20min walk on the treadmill as well before work.
A couple of weeks ago a college convinced me to join the 7km Sun Run. walking not running, which Im still finding very daunting.

Can anyone give some tips on preparing myself as the day is quickly arriving? What Im best doing with my exercise and the night before perhaps?

Also I am raising money for a great charity if anyone is interested, Im very proud of myself for committing to this.
Its raising money for Monika's Doggie Rescue.
www.everydayhero.com.au/saveapuppy