Today I installed Subversion  on my Synology DS209+ NAS. A very good point to start is this  step-by-step tutorial written by the guys of Synology. Installing Subversion was/is very easy because there is an IPKG package available which will download and configure all dependencies for you. If you don’t know how to install IPKG, just read this blog .
To understand a bit more of how Subversion exactly works, visit this  website, where you can download a free e-book in a lot of different formats (like pdf / HTML).