Can someone PLEASE give me some pointers on Shipcalc Partners *.inc

For the past 3 months i've been working on building an Ecommerce site for my mum's shop. I've got the design, and my mum has posted about 150 products. We're all set to go - except for a working shipping module. Ecommerce uses the Shipcalc contributed module to apply shipping costs at checkout time and add them to the total. To do this, Shipcalc uses "partners", which are shipping services that are accessed via an *.inc file in the "partners" directory of Shipcalc.

Unfortunately, unless you live in the USA or Canada, there are no "partner" files to be used. I live in Australia, so I need to build an *.inc file that will access the Australia Post Delivery Rate Calculaor API. There was a feature request for Shipcalc filed earlier in the year asking for this *.inc file, but it never got anywhere. My initial efforts to make one are documented at the bottom of that thread ... but I've only started a crash course in PHP a few days ago, so my first attempt was a bit dumb. In any case, I think I'm getting close.

Can someone who is familiar with Ecommerce module, and especially Shipcalc, please take a look at my *.inc file and those previously mentioned threads, and give me some pointers on how to get it working (I'm able to create configuration and product options and save them - basically everything works except the _get_rate function)?

i'm at my wits end, and will soon have to abandon drupal (os_commerce provides and Australia Post shipping API - d'oh, if only i knew this was gonna be such a nightmare), even though we've put so much work into it :(