Paypal Cart Integration

I need Someone with experience in working with paypal carts (where customers adds digital documents to cart and downloads) - essentially there should be an admin section to track sales / customer details etc. Also they should be comfortable working with databases (MySQL), PHP etc

I have already installed an application (php) paypal cart and download manager (for selling pdfs) onto clients existing website, but there are a few issues which app support are not respopnding to..

clients website is on a Windows server not linux

I need someone to take charge of this and get something resolved as soon as possible.