OScommerce One page checkout correction for STS compatability

We have a script for a one page checkout [login to view URL] contribution 6646 v1.03 for relevant files. Whilst it appears to work on a heavily modified osc rc2.2a site it currently doesn't work 100% in sts mode. The main issue is to get it so it functions the same in or out of sts mode(as it was originally intended to work). The change shipping and billing address buttons do not work in sts mode and currently the billing address is blank on first page loading. This should take about an hour to a day at the most for those that have experience with sts, java/ajax/ php and oscommerce rc2.2a modified sites. We are looking at establishing a link to a reliable programmer that can help with future projects. The solution must be shown to be working on our system for satisfaction, a brief explanation of how you got it to work would be appreciated. If you require further details please do not hesitate to contact us via getafreelancer