So, here's what I need to do.

I am creating a portfolio pag. The portfolio page will be an image map where clicking the logo of each client company will spawn a floatbox window to show off the specific content I have created for my clients. Follow so far?

Here's what I need to do --

When the user clicks the company logo of my client, it should spawn the floatbox window with an image that shows what I've done for that company. Since I have done a great deal of work for some of these clients, I will want to show several images for some of them (i.e. web site, brochure, logo).

When you click the logo for Client A, floatbox will pop up with to show the logo I designed. I need clicking "next" to take the user to the next thing I made for that same client, say, the brochure, even though there is no direct link to that brochure from the main portfolio page. I don't want clicking next to take the user to the next client. Each "mini-gallery" needs to be navigable but limited to only the work I've done for the particular client. So, essentially, clicking the logo will bring up a floatbox mini-gallery of work I've done for that client. Clicking another logo will do the same for another client. But you won't be able to move between clients from within the floatbox pop-up.

Does that make sense?

Thanks in advance.

What you want to do is to create a gallery of images for each client. Each image in the gallery will be defined in an anchor on your page, but the anchor does not have to have any displayable/clickable content itself. You would use a unique group string per client. See this post for a short example.

You have one complication. You mentioned starting from an image map. This will work fine, but there could be a numbering problem. Anchors are "tagged" before area maps when floatbox starts, and the gallery order is based on the tagging order. So if your additional gallery set items are anchors, but the clickable thing is from an area map, you will be opening your gallery with the last item in it. In other words, it will start with "image 12 of 12" and clicking next will take you to "image 1 of 12".

You can get around this numbering problem by putting all your gallery items in empty anchors on your page, including the first gallery item. Give that first gallery anchor an id, let's say id="client1". Now instead of giving your area map thingy a class of "floatbox", give it an onclick action that will start your gallery, like this:
onclick="fb.start(document.getElementById('client1')); return false;"

I hope this makes a little bit of sense.