Wow, 4 people have posted while I've been typing this... Anyway-
Heh, I never dug into XP, sorry... I used up that good ol' trial a few years back, and then sort of slipped back into 2k3.
Judging by the look of the tileset, though,
it looks like the exact same mapping dilemma I had with FSM. Notice how you have these following possible candidates for your thick forest --->Not just the top one!!!<---:
Think of those as convex (the bottom ones) and concave (top one) possibilities for your jungle. Work out a rough idea of what you want the landscape to look like with just simple grass (don't make it a square! It makes it more fun that way, and doesn't aggravate people), set up your trunk tiles on the second layer all along any of the back borders you may have (at least I think... Like I said, I don't use XP. You'll want to make a sandwich with the leaves and the background), and now the magic begins.
Of course, I can't show with pictures without a functioning copy of XP, but Joy did indeed post a perfectly good example on the screenshot thread (and her tutorial will be a lot more helpful, just as long as you're good to her in the mean time). Take another good, hard look at that map, it'll explain a lot.
I know a text-based explanation can't get most people far, so either do the lazy thing and wait for Joy to take care of you (again), or do the smart thing and use what she's already given you. Practice by making a replica of that map (not exact, of course, that's plagiarism. Even for maps.), then make a couple of your own before you even think about putting one in your game.
Get used to which tree tile goes where, work out every rough area of your map, and
practice by making a couple more. It may be frustrating at first, but you'll be slapping yourself later when you bust out 5 awesome, diagonal maps.
I guess sometimes you just have to figure things out for yourself. OR you can figure things out using what people have already given you; whether it has a "Tutorial" label on it or not.