axlrose :
my understanding is the only thing the dell really beats the gateway at is the color gamut and that's only useful (as far as the differences between the two) if you are into hardcore photo work.
i've never seen any lag on the gateway playing bioshock (first person shooter) at 2560x1600.
As far as colors go, yes, the increased color gamut makes it better for photo work. It also makes it overall appear more vivid, and it can display more total colors. Trust me, this is visible. I can see a noticeable color difference between my monitor (92% color gamut) and my dad's 2408 (110% gamut). The 2408 just looks more vivid overall, and the colors really pop out at you. The 3008, at 117% color gamut, must be incredible to behold. The gateway is cheaper though.
As for 1080i, 1080p, and 30", the 1080i is interlaced. This means that it is at a resolution of 1920x1080, and every other line is refreshed 60 times per second (first the even lines, then the odd lines), making the entire picture only refresh at 30Hz rather than 60, as it takes 2 "frames" to fully refresh. 1080p is the same resolution, 1920x1080, but is refreshed 60 times per second, every line. 30" monitors beat either one however, at 2560x1600, with every line refreshed at 60 times per second.
As for the dell costing more? Dell actually has 2 models, the 3007, which is the older one, that goes for $1200 or so (great budget 30", if there is such a thing, can't quite stand up to the response times and color capabilities of newer ones though), and the 3008, which goes for $1800 or so. The Dell also supports DisplayPort, and if the HD video that it supports is low quality, that's certainly news to me (it looks stunning).
Of course, they're both amazing monitors, and you certainly wouldn't go wrong with either one.