gravitation...

[Nullpunkt]

Can't tell you any more than you already know, sorry. But I do know what it is, and I have a friend in Vermont who's collecting the DVDs. Pretty cool, Gravitation. I'd like to see it.

[Mahaado]

The OVA is basically just a side-story to the series. It doesn't really continue the series. It's more like an extra episode than anything else. You can not watch it and not be missing anything.

I've only seen it once, but it does have more Ryuichi and Tatsuha in it, so maybe it's worth it just for that?

[SnowDemon]

I've seen the OVA, have it on my computer too (downloaded a long time ago). It really is just like an extra episode. However, I did like the series more, and you're not really missing anything by not seeing it. But yes, it is actually worth checking out if you get the chance. Anyway, good luck finding it.