Theme issues
I've very recently set up a 4.5.1 rig and all appears to be fine, except in the themes department.
Bluemarine appears fine, as does manji (with phptemplate installed).
However chameleon, marvin, marvin_2k_phptemplate, persian, pushbutton and sunflower all appear awash, lacking any solid colours, broken layout etc. as if the CSS is not working properly. The css links are correct however and will manually download fine. Incase firefox was going mad I fired up IE as well with the same results.
Also, importing the trip theme causes an error when loading the Administer -> Themes page:
Fatal error: Class theme_trip: Cannot inherit from undefined class basetheme in /webs/drupal-4.5.1/themes/trip/trip.theme on line 5
Any ideas?

Trip is outdated
You should only use themes and modules that match the Drupal release you're using (4.5.x, 4.4.x, ...). Perhaps it is conflicting with the theme system.
Half of those I've listed
Half of those I've listed are included with the 4.5.1 release.
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Dax!