We moved to source control about six months ago. Subversion took about three hours to learn, and it is free, and there are easy-to-use tools available for Windows and Mac (Tortise for PC, Textmate etc. for Mac).
Subversion (and other source control products like CVS) let you check in and check out your code, but instead of locking a file, multiple users can work on the files at the same time. The program is smart enough to merge the versions successfully most of the time, and when it can't, it lets you know so that you can resolve the conflict. More importantly, you never need to worry about having the latest version of a file or overwriting someone else's change.
Source control reduced our versioning conflicts by about 99% and has saved us countless hours. I am really ashamed for the years I spent without it. Do yourself a favor, all you Dreamweaver users out there, and try it out.