PHP, Paypal and Flash (and https)

As it stands, the only info I can find about integrating flash and paypal is about using a custom shopping cart. I have built a shopping cart that fits my needs. Now I want to build the checkout section, but can’t find any info on this. I do NOT want the customer to be taken out of my site. I want to collect the info and have php send it to paypal. Any thoughts?

Also, I can’t find a good explanation of secure connections. If I use a loadVars like this:

myLoadVars.sendAndLoad("https://mysite.com/phpform.php", this, "POST");

will the info I send be secure? I have a certificate on my site, but I can’t find info on how it is used.

Does this make sense?
-Joshua