It's not attractive as such, but it's clear and functional. As far as installing another phpbb theme go for it make a few diff headers up to suit and alternate them if you are not completely happy with the current one .. Ask your userbase for an opinion you have 66 users they should be your main crits but thats just personal opinion ..
I say it looks better if you can put the background a little light orange ish color to go with the page.
I think it looks fine, could maybe tone the orange down slightly, but apart from that it's easy to navigate and laid out well.
i know, im trying to fix the template, the register page was showing up blank and i dont know whats wrong, still working on it