Custom Field Issue

I have 2.7 installed, but this was a problem in earlier versions too. When I click to add a post, the page take FOREVER to load. Then I noticed that the custom field area was adding HUNDREDS of (mostly duplicate) fields. I think this is because I imported this blog from another WordPress blog, and it took me a few tried before it worked. How can I delete all these extraneous custom fields so I can post? I would be willing to issue a user / pass to someone who could help me trouble shoot.

Thanks, JC