Hey, can anyone recommend a URL (or website) where I can download a basic (or old) UNIX OS that will run on an ancient laptop that has a 386 processor, 4MB of RAM and a 40MB harddrive? Your help and suggestions are much appreciated! 
What are you planning to do?
You can use a small BSD like picoBSD and EmbeddedBSD. You should also be able to get NetBSD to run on such a small HD.
You could probably get Debian or Slackware Linux on it as well. The big thing I guess would to install minimal with just the binaries.
You should look for older versions of SCO Unix or Sco Xenix 386 System V. It is out there and as basic as it gets. Unix has not changed much.
http://old.lwn.net/Distributions/
this is a list of 283 Linux distributions, look under special purpose/mini and floppy distributions.
this one should work: http://jailbait.sourceforge.net/
Of course everything related to what do you plan to do.
Try ftp://sunsite.unc.edu/pub/Linux/distributions FTP ste. There are a lot of distributions. You can choose what from them match to you.