I want to amend the section that shows the avatar etc. Can someone tell me which file to edit. I'm fairly sure I can find my way from there.

Also, how do you edit the drop down menu text colour?

Thanks!

that would be the template file: newbb_thread.html

located at xoops/modules/newbb/templates/newbb_thread.html

to edit this file. you can edit it manually and upload it back on to your site.. and i think that may also require a module update. (that refresh kinda button in the module admin section).

or you can clone your template set and modify the one you cloned and. also have to set your site to use the cloned template set to use it.
http://www.macambridge.com/dummies/themes.htm#How%20to%20clone%20Templates:

hope that helps.