Build my own shopping cart widget

Hi there.

I'm looking for some help literally taking apart and rebuilding the shopping cart widget. I just want a custom widget which will show the total number of items and the total cost. You can have a look at the top right of this page I am working on to see what I mean:
http://www.screencandy.co.uk/myss/

You can see that I have almost got it working - the shopping cart shows the total number of items in the cart, as well as a decimal display of the total amount in the cart. In this case, it shows 0.5, which is correct because I have only one item costing £0.50 in there.

So, my main question is how I can display this cart total in correct currency format.

As a wider question, if there anywhere I can see something like a list of all the functions that MarketPress uses to display the cart - For example anything like: mp_items_count_in_cart

I hope this makes sense! I hope you can help me.

All the best,

Neil