Going to your site makes Dante Alighieri's
The Inferno come to mind, except instead of hell, it's
HTML Hell I'm journeying into. Where to start...?
First, get rid of the animated Pokemon sprites. It is usually a good idea if buttons on a menu have some sort of indication as to where they actually go. For example, a "Register" button should have some indication that it relates to registration, usually accomplished by having "Register" written on it. A flashing Raikou, however, means something totally different than "register" (it actually means "I don't care one bit about good web design guidelines, so I'll just stick flashy pokemon on here because it's a pokemon forum", which isn't even close). The fact that they're animated makes it even
worse simply because it distracts from the content (that, and having numerous animated gifs playing at once on a page looks choppy).
Consider this: The flashing Raikou is 14 kilobytes. That's 14,000 bytes, give or take. The word "register" is 8 bytes. Which means you're effectively wasting 13,992 bytes with a graphic that has no business at all being a "register" icon, flashes distractingly and is more resource-intensive than an eight-letter word. You might be all "what's the big deal", but flashier isn't always better. Same goes for all the other stupid animated sprites on your menu. Get rid of the "
Mystery Meat Navigation" please.
The other icons you use, namely the Pokemon Trainer sprites, do not fit at all. They are 64x64 and it looks like 30x30 is the largest you'd want an icon to be. The table isn't expanding to fit the sprites, either, so parts of them are cut off and, on the thread index, they run into the thread titles. This looks horrible as a whole and you should either cut the bodies of the sprites off (if you're trying to go for the Pokemonish theme, maybe the head only would look better) or find some actual forum icons.
The style is incomplete. The table bodies are grey (standard phpBBish) while the outside is green. Doesn't look all that good. Maybe you should change the rest to some form of green so that it all looks coherent.
Get rid of the animated background image. Animated backgrounds are a sign of
amateur website design, they are distracting, and they are larger than necessary (this one is 100KB). You could just set it to green and leave it at that.
Maybe I'm expecting too much out of you. After all, these
guidelines must be so boring to read. Who cares about clean, nice layouts when you could have flashing sprites and blinking backgrounds? But it's a truth, the best websites have clean layouts. There's a site out there that probably every internet user has ever heard of. It's called
Google and is a good example of clean user interface design.