http://hce.halomaps.org/index.cfm?fid=3434
How do I convert those into tags?

You're going to need to rig the model, animate it, compile the model and animations, compile the bitmaps, copy an existing weapon tag, replace the model, animations, and bitmaps, and save.

All right thanks!
Didn't know you had to rig it.

depending on how much the weapons are edited, you might get away with simply.
importing the regular h1 weapon and its markers and nodes with the gbx model importer (get v2)
aligning your h3 model with new bitmaps applied
deleting the h1 weapon
linking the new model the same as the old one was
export
make shaders

eat strawberry rhubarb pie.

I'm sure UnevenElefant5 still has his tutorial on rigging models and setting up shader regions. At least, that's how I learned it. Go bug him if you need help :D (not too much)

These H3-ish weapon models by tazz have already been converted into weapon tags a long time ago, I'm sure you can find them on the Halo Filefront website, they are weapon tags but for Halo PC. You have to extract them from the Halo PC map file and reroute the tag directories.

Yea, I converted them but lost em. They have no animations so it doesn't help

They're modified Halo 1 weapons, so I'm assuming that Halo 1 animations would fit them.

So you're Jackal from H2 Filefront?

Jackal rigged them to FRain's animations. Just because he "converted" them doesn't make him Jackal. Jackal's much cooler than he is :D