I adapted a bit of code that I found somewhere, to give me a conditionally fixed sidebar (it remains fixed unless you scroll all the way to the bottom of the page, where it gets bumped up by the footer). It works on a static page with self-contained code (HTML, CSS and Scripts in one page except for the call to JQuery 1.3.2):

A Static version of the page is here, working

It may not be the best written piece of code -- and suggestions for improvement I would appreciate too; 

--but mainly my problem is re-writing it in the correct syntax (I assume that's what I have to do?) so it will work as a linked script in a system like Tumblr or Wordpress. I've tried pulling apart other people's scripts to see the correct way to call it but I'm still doing something wrong. The weird thing is Tumblr is so much easier than WP in that it's all in one file, and yet taking the same structure you see in this static file does not work on a Tumblr site any more than in WP. I don't know enough to solve this on my own.

It is a very short routine but I can't get any further with it. I'd consider paying someone to fix it at this point but I don't know where to go for that either. Apologies if that's considered inappropriate in this forum.

See lunelson.tumblr.com for the same structure as a tumblr theme, otherwise hideously ugly as I just started putting it together with dummy content...