I'm editing the Death Ray from MZ at the moment, and it has around 400 animated glob parts that I want to have removed. But it takes around a minute for my machine to actually remove one. So I was wondering, is there a way to select multiple NiTriStrips?

that would be news to me. I don't think so.

Ah bugger.

Next question. I saw a picture of a weapon that fired from two barrels at once. Does this mean it's possible to have multiple Projectile Nodes?

Here's the mod with the pic: http://www.fallout3nexus.com/downloads/file.php?id=6310

I'm not sure about the current version, I haven't really worked with it much, but if you right click on a section you should have an option to remove the entire block, not just the individual components. That's how it used to work anyway.

But the problem is that I have around 400 blocks.

it might be easier to open it up in blender and remove it that way (select the parts you want, then do an inverse select to get rid of the parts you don't want).
i don't have MZ installed, but would you mind posting a screengrab of the NIF (just the tree structure should suffice)? it would be easier imo to suggest solutions.

CTRL+DEL can remove multiple.

No. It is impossible. It must be mimiked by putting the projectile node between the 2 barrels and have a custom projectile that looks like it is 2.

i'm not sure but it might be possible. http://www.gamesas.com/?showtopic=1031756 may shed some light.