no, GT & GTX are the different models of the nVidia cards, that we've been discussing in this thread... some have suggested the 9600GT, which is a newer model, of the 9xxx series, but is a upper mid level card. others have suggested the 8800GT, a revised version of the 8800 series. in the 8800 series there is the 8800GTS 320MB & 640MB, & 768MB 8800GTX & 8800 Ultra based on the G80 core (also listed them in order of performance from low to high), then came the G92 cores, revised & improved upon G80 cores, in this 8800 series there is the 8800GS 384MB, 8800GT 256MB, 512MB & 1GB, 8800GTS 512MB & 1GB (also in order of performance). Now there is the Geforce 9800 series that replaces the 8800's, although they use the same G92 core, currently there's only the 9800GTX & 9800 GX2... the 9800GTX replaces the 8800GTX & Ultra's, though spec wise is practically the same as the current G92 8800GTS, it adds 2 SLI connectors like the 8800GTX/Ultra has, so you could run a Tri SLI setup with them, which wasn't possible with the 8800GTS.
But you could easily find out more about the cards by going to Wikipedia & using search terms like "Geforce 8 series" & "Geforce 9 Series".