Photonic torpedoes seemed all-new (perhaps even developed as the direct result of data Archer sent back after "Sleeping Dogs"?). Phase guns might have been old in the 2150s already; the one thing new about them in ENT would be miniaturization to sidearm size. Pulse cannon in turn were only ever mentioned to be part of the NX-02 arsenal, and possibly never seen in action.
Which leaves all sorts of possibilities open about the armaments of Starfleet vessels prior to ENT. Just spatial missiles and plasma guns? Those plus phase guns? Something that had already gone out of fashion altogether by 2151, such as railguns or lasers or glass bead clouds or microwave EMP guns?
Earth might have been forced to develop its own space guns if Vulcan considered it advantageous to maintain a trade embargo on interstellar-standard weapons. We never really heard of an actual embargo, though, so the early UESF might have bought modern armaments from the first space traders to offer them. But apparently the Boomers were in the business of buying weapons, too, and they never got anything better than plasma guns (plus hand phasers!), so perhaps nobody was selling.
One would assume Earth or its nations had starfleets early on, at least since the 2070s, and non-starfaring space fleets before that. Archer's organization might be fairly recently founded (Archer tells he was born before the founding, in "Horizon"), but that doesn't mean there wouldn't have been Earth starships operated by military organizations before this.