I was watching the DS9 episode Tears of the Prophets recently and in the scene where the Federation was about to conquer Cardassia, I noticed that one of the ships looked exactly like an NX class ship. Has anyone else noticed that, or am I just mistaken. I'm sorry that I don't have a screen shot of it, but I was hoping that there might be someone that can confirm or deny this for me. Thanks!
DS9 ended two years before ENT debuted, so the odds of an NX-class ship in the former is kinda, well, zero. As Pavonis said, you might have seen an Akira-class ship since the NX-class was based on that design and modified.
Akira-class ships were indeed visible in Tears of the Prophets. In-universe, I suppose we have to assume that the Akira design was a homage on the part of Starfleet to the NX-class? In reality, the NX-01 was based on the Akira design, which was first introduced in First Contact.
Starfleet does homages? Doesn't sound all that likely. The common design features between the two would appear to be the use of twin booms, the inclusion of "turbocharger caps" on top of those, and a bow cut in the saucer. The last is the least "homage"-like of the features, as it is typical of all the ships we first saw in ST:FC, and has for several decades been a fan favorite for making the neutrally round saucers look more menacing... Twin booms are found in many fan or RPG designs, too, and indeed NX most closely resembles FASA's Loknar class in configuration (although Loknar had the forward ends of the booms underneath the saucer rather than atop). So the "turbochargers" (a feature borrowed from the twin-boom P-38 Lightning fighterplane of WWII for purely aesthetic reasons) are the one unique connection between the ENT and ST:FC/DS9 ships. A deliberate one in Paramount terms, of course, but do these fancy shapes perhaps also fill the same fictional function in NX and Akira in in-universe terms? As could be expected, those features were never assigned a clear on-screen role in either version. At one point, the Enterprise spat phase beams out of them, FWIW... Timo Saloniemi