I have seen people running openblocks on their server, but there is no information on where to download it and how to add it.

Sure there is, it's right on the front page.
https://github.com/OpenMods/OpenBlocks

v1.2.5 for Minecraft 1.6.x You'll also need OpenModsLib.

For stable release downloads, click here.
For snapshot versions, check the Jenkins.

Two things, is it the same for client, and is there a version for 1.5? (is that considered a snapshot?)

It's always the same for the client, all mods are universal since MC 1.3.
1.5 is not supported and we will not supply bug fixes for it. However there may be a 1.5 build on Jenkins. You should really consider updating, but I'll see if I can find an old version for you. One moment.

It would seem there are no builds for 1.5.
1.6 has been around for a long time. You will need to update

Ok thanks.