Nope, you definately can't use those features.
At this current point in time, Valve's suite of Source powered stuff is completely seperate. HL2, CS:S, DoD:S and Episode One all run off one version of the Source engine (which
might be split into various builds, depending on the game). The HL2 engine was updated when Episode One came along, but none of the maps were recompiled to take advantage of the changes. The upgrade that Episode One brought wasn't that large: it was more of a modular upgrade than anything else.
The Orange Box brings with it a new version of the Source engine, one that's totally seperate to the previous version. Basically, Valve will need to unify the games under the new engine, which, I imagine, will be total hell: they're not exactly reknowned for their file efficiency at the moment. Maps will need to be completely recompiled to work under the new engine, meaning that everyone will need to download a crap-tonne of content to replace the old one. As well as this, there's going to be problems for players who can't get the Orange Box engine working properly either.
It would be nice if they did it slowly, but tbh, I have no idea where they'd start.