I just noticed today that Lavasoft has stopped supporting Ad-Aware SE Personal, and in order to get newer definition updates, you must upgrade to Ad-Aware 2007. I was wondering if there was a site where I could download updated definition files, without upgrading to the latest version. Thanks for any help!

Manual updates still in same location:
http://download.lavasoft.com/public/defs.zip

Thanks for your help! Is it possible to have it find the update when I click on 'Check for updates now', or do I have to do it manually from now on?

I created a little batch file (automatic command) that copies the REF file to where Ad-Aware lives in ProgramFiles

But actually, are you saying it won't auto update now?
Well maybe it's time just to download the new free Ad-Aware (http://www.lavasoftusa.com/products/ad_aware_free.php)
That would be wiser (obviously un-install the old one fully first)

I don't mean to hijack this thread, but I am on a very slow dial-up connection. Each time I go to update the definitions, it takes about 1`5-20 minutes. Usually this is about twice a week. Why do these updates take so long? Is it starting everything from scratch?

Yes it is (starting everything from scratch)
This applies to just about all Spyware programs

AntiVirus programs (on the other hand) just have updates (on the automatic side)

Also ALL manual updates (both Spyware and Antivirus) have the entire signatures from years ago until now. (Note: some sites do have small update files, like AVG)

Ad-Aware SE Personal: if you had the paid version, you can continue to manually update by clicking on the 'world', top right of the screen.

Yes, but doesn't it update the ref file completely (with a whole new ref file)

The new Ref file being everything that Ad-aware has ever found