Some of that (changing the colors of the text and whatnot) you can do with CSS styles. The rest (changing the actual text) requires that you use a scripting language like Javascript.

For the...

Actually, using HTML would make the project impossible, not more difficult.

HTML (along with CSS) is just a way to mark-up and present information. It helps you organize content on a website.
...

You need to change the quotes around your doctype stuff. Notice how they slant in and out? That's a special type of quote (probably created an an escape sequence), that doesn't work for quoting...

Building a forum from scratch would be an interesting project... but long and unnecessary unless you're really interested in learning how to do it.

If you want to get something off the ground...

I think that paints the problem with far too broad a brush. Why would you have to get rid of all hover images in order to be handicap accessible?

Example. A hover image could be used to change...

Not sure if there's any way to do this in a real drop-down menu, but you achieve something similar with a little out-of-the-box thinking.

Instead of using a dropdown form item, build a css menu -...

And to take this one step further and answer the original question...

I'm thinking you need to change

.ivt ab:hover {
to...
.ivt a:hover b {

In the original example, you're looking for a...