Ok so the scenario is as follows.
Have a WSS site hosted on Microsoft Online and what I am looking to do is integrate it with xero.com the Sharepoint has a list called Jobs with the following columns:

Title
Customer
Customer Description
Job Type
Priority
Assigned To
Status
Due Date / Time
Start Time
End Time
Engineer Notes
Location
Invoicing Description
Invoiced
Month
Purchase Order No
Created By


Additional columns will be added such as Rate, Total, etc
The end point is https://api.xero.com/api.xro/2.0/Invoices
This requires the following information to be Posted or Put to the site after authenticating and using the Callback URL to my site. Xero.com has code samples here blog.xero.com/developer/getting-started/code/
<Invoices>
<Invoice>
<Type>ACCREC</Type>
<Contact>
<Name>Martin Hudson</Name>
</Contact>
<Date>2009-09-08</Date>
<DueDate>2009-10-20</DueDate>
<LineAmountTypes>Exclusive</LineAmountTypes>
<LineItems>
<LineItem>
<Description>Monthly rental for property at 56a Wilkins Avenue</Description>
<Quantity>4.3400</Quantity>
<UnitAmount>395.00</UnitAmount>
<AccountCode>200</AccountCode>
</LineItem>
</LineItems>
</Invoice>
</Invoices>

Am basically looking for some help to get this up and running.
I am new to development but understand the basics, have looked around at tutorials but have not been able to find anything relavent.