Could anyone help me resolve the differences between these two BMX bikes? I'm deciding between those two bikes and since I'm not a pro, I cannot spot many differences. I was hoping you guys could help me out.

One notable difference I know of is that Mongoose Capture 11 has more rims than its competitor, I hope that's a good fact, right?

Mongoose Capture 2011 specifications:

Frame:  Full Hi-Ten
Fork:   Full Hi-Ten
Crank:  3pc Tubular Cromo, 170mm,33T steel chainring
Bottom Bracket:     Mid Sealed Bearing8 spline
Speeds:     1 Speed
Cog Set:    Odyssey 13t freewheel
Wheels Size:    20"
Rims:   Alloy 36H front, 48H rear
Hubs:   36H Steel, 3/8" axle
Tires:  Innova (F&amp;R) 2.125
Pedals:     Mongoose Nylon Fiber
Brake:  Pro Rush with Pipeline cable
Handlebar:  Mongoose Hi-ten 7.5"
Stem:   Mongoose Front Load50mm Ext.
Headset:    1-1/8" Ahead
Brake Levers:   Rush RX402 hinged
Spokes:     ED Black Steel
Grips:  Mongoose Kraton
Saddle:     Mongoose Slim
Seat Post:  25.4 straight steel
Seat Clamp:     Alloy single bolt slim
Extras:     1 pair axle pegs 


GT Slammer 2011 specifications:

Type of Frame   GT freestyle design, Steel tubes, DT gusset, American BB, seat stay mounted U-brake, GYRO cable guides
Fork    GT freestyle design, hi-ten 1-1/8" steer, 31.8mm hi-ten blades, 6mmT. Dropouts
Crankset Chainwheel     Forged steel one piece crank, 170mm / 33T steel GT design
Bottom Bracket  American loose ball type
Cog Set     DNP 13T. Cr-mo
Chain   KMC Z510
Rims    Alex G303, pinned aluminum, 32F/36R hole
Front Hub   Steel body, 3/8" heat treated axle, 32 hole
Rear Hub    Steel body, 14mm hi-carbon axle, 36 hole, single FW threads
Spokes  14G
Nipples     Brass
Tires   GT Air Bags, 2.1"
Pedals  GT Jump design, PP material
Front Brake     Rush 900D, aluminum Caliper
Rear Brake  Rush 933D, aluminum U-brake
Brake Levers    Tektro 289A full aluminum lever and clamp
Handlebar   GT dirt/street Steel, 7" rise
Stem    GT freestyle drop design, machined GT logo
Headset     1-1/8" threadless, steel
Grips   GT Wing shroom design
Saddle  GT Slim mini street design, 8mm rails
Seat Post   Steel, 25.4mm x 200mmL.
Seat Clamp  Alloy Single bolt
Extras  SST ORYG, one pair GT 36mm OD x 97mm forged steel pegs


UPDATE

After what @mathew suggests, I have found 2 other competitors:

GT Performer 2011 for $369, of which the description says:

Type of Frame   GT Freestyle Design Frame with Cr-mo main tubes, machined 1-1/8" headtube, 19mm CS, DT gusset, Mid BB, seat stay mounted U-brake, and GYRO cable guides
Fork    GT freestyle design, Cr-Mo 1-1/8" steer, 31.8mm hi-ten blades, 6mmT. Dropouts
Crankset Chainwheel     GT tubular Cr-Mo 3pc., 8T spline, single bolt clamping, 175mm / 25T steel GT design
Bottom Bracket  Mid size sealed bearings, 8 spline Cr-Mo axle


Versus Mongoose Article 2011 for $329, which has:

Frame:  CromoFront Triangle
Fork:   Cromo Steerer
Crank:  3pc Tubular Cromo, 175mm,25T steel chainring


Is any of these latter two better/worse, or are they the same?
The heart of a bicycle is the frame - even on a BMX. Both of the models that you are looking at use high-tensile steel rather than steel alloyed with chromium and molybdenum ('cr-mo' steel).

With a normal bicycle made of high-tensile steel the problem is the weight - the frame (and fork) weighs significantly more than it would be if it was made of a better 'cr-mo' steel.

On a BMX bike the problem with high-tensile steel is not just the added weight. High tensile steel bends whereas 'cr-mo' steel flexes. You need this flex if the bike is to survive crashes as well as intended heavy impacts.

Given that there is a premium attached to 'cr-mo' frame/fork many manufacturers replace one or more tubes in a high-tensile steel frame with 'cr-mo' tube(s). They can then put a sticker on the frame claiming it is 'cr-mo'. This gives the impression that the frame is 'cr-mo' when it might be mostly high tensile steel. Therefore, when comparing bikes, look at the frame and fork to see how much of it is 'cr-mo' and how much of it is high-tensile steel. Get this detail right and go from there. Components can be replaced - if the bike comes with cheap plastic pedals then you can upgrade them to something more desirable when they break for a modest amount of money. So get the frame right and look for something with 'cr-mo' at least in the main tubes. 

EDIT:

The GT Article and the Mongoose Performer are very similar in specification. The separate seat clamp on the GT is a neat touch, the frame also appears to be chrome plated rather than painted. Personally I prefer the chrome plating as it can be polished up very easily to remove rust spots whereas the painted frame shows damage that bit more evidently. There is little to choose between the components, so on the basis of the chrome plated frame I would check that it is (and not just painted silver) and go from there.

The slight complication and opportunity is with the pricing. There are new 2012 versions out of both of these bikes. Some dealers may therefore want to discount the 'shop soiled' 2011 models that they have in stock so that they can get the 2012 models in. You may want to look at the differences in the model years to see what those differences are, maybe it only comes down to paint scheme, but, with a bit of shopping around, you might be able to get yourself a deal.