Can't get checkout to work.

I've been working on this for 2 days now. I'm new to eCart and not very adept at PHP.
I'm using site root linking for paths
My gateway is Authorize.net. I have their doc's in hand.
I'm testing on a localhost Apache server using php. I can't get curl installed on my Vista local host, but I suspect my problem begins before that dll is req'd.
I've read all related eCart Tutorial and help docs as well as Authoize.net integration doc.

When I use all defaults on the Display Mgr and Checkout wizard. I get into cart.php and from there to checkout.php np, but cannot go further than that. When I click the checkout button in checkout.php, I get a blank screen. One reason I thought was that there is no link to Authorize.net using the checkout wizard (beyond the transaction login info), so I use the Insert Checkout Form button's-->local checkout option.

This form yields all the fields needed for Authorize.net transaction processing and agrees with their integration doc. I save the form as Checkout.php, overwriting the wizard's form with a new checkout page. I get into the cart okay, but now I can't go beyond that.

I suspect the problem has to do with paths, so I searched out every path in these two files and made sure it was site root relative. No help. I've been nosing around in the include files looking for clues too, but don't see anything I should mess with.

I delete everything (including eCart subdir) and start over. Problem loops back to where it began. I've done this maybe 10 times now and its got me stumped.

Ideas? Please!
Thank you.