Using Same Checkout/Payment across Multi-Store/Domain set up

[tkovapor]

So, I'm setting up 2 different, separate domains within my Magento (1.8.1, I know, older, but upgrading is a whole other issue I won't get into right now). One if wholesale, one retail, and I want to share the same checkout/payment processing on both sites. But both domains have to be completely independent until checkout. I've looked through different tutorials and forums, and have not found a solution that truly explains how to do that (right now, the home page on the retail site isn't working either, but that's a different issue I'll tackle elsewhere). So, can someone help or point me in the right direction on how to configure this, in detail? Assume I don't know anything about programming beyond modifying CSS/HTML to make changes to the look and feel. Let me know if you need more info from me, too.

[tkovapor]

If it helps, it looks like I can get at least the categories underneath the second domain name to display correctly. However, I get a 404 error when trying to go to the home page (but the correct theme displays, just not the home page).

[tkovapor]

Anyone have an option on how to make this work? I just want to redirect from one store to the other when someone goes to checkout, so that all checkout processing is through one URL, not two different ones. How would I do that?