How great is the video card in the iBuyPower? From what I've read, the GTX 260M is comparable to the 9800M GTS in the Gateway - but this machine just has a GTX 260? Does anyone know the difference?

I have about $2000 to spend - but I really, really, really don't want to spend that much if I don't have to. I'm looking for the biggest bang for my buck. One year down the road, I still want to be able to play most new PC games at decent settings. I would rather not pay my max amount for an overpriced brand name machine - even though I have included a couple them. I just want a nice gaming desktop replacement.

These are some models and configurations I've picked so far - I need some opinions, because I am no expert. I've read a million notebook reviews for each one, but I'm still indecisive. It would be great if someone could help eliminate a couple of options for me. These are not what I'm limited to - if you know of a machine that I might want to take a look at, please link me!

Options so far (from least expensive to most):
These are copy/pasted specs, let me know if you need more info.

1. Gateway P-7805U FX Configuration: 1149.99
Processor: Intel® CoreTM2 Duo Mobile
Processor Speed: 2.26GHz
Graphics: NVIDIA GeForce 9800M GTS
Video Memory: 1GB GDDR3
System Bus: 1066MHz
Cache Memory: 3MB on die Level 2
System Memory (RAM): 4GB
Type of Memory (RAM): DDR3
Hard Drive Type: Serial ATA (7200 rpm)
Hard Drive Size: 320GB
Optical Drive: Double-layer DVD±RW/CD-RW

2. MSI GT725-074US: 1349.99
CPU Type Intel Core 2 Duo P8600 2.4G
Memory Size 4GB DDR2
Hard Disk 320GB
Optical Drive DVD Super Multi
Graphics Card ATI Mobility Radeon HD 4850
Video Memory 512MB DDR3 VRAM
CPU Type Intel Core 2 Duo
CPU Speed P8600(2.40GHz)
CPU FSB 1066MHz
CPU L2 Cache 3MB
GPU/VPU ATI Mobility Radeon HD 4850
Video Memory 512MB DDR3 VRAM
Graphic Type Dedicated Card

3. MSI GT725-075US: 1599.99
CPU Type Intel Core 2 Duo P9500 2.53G
Memory Size 4GB DDR2
Hard Disk 320GB
Graphics Card ATI Mobility Radeon HD 4850
Video Memory 512MB DDR3 VRAM
CPU Type Intel Core 2 Duo
CPU Speed P9500(2.53GHz)
CPU FSB 1066MHz
CPU L2 Cache 6MB
GPU/VPU ATI Mobility Radeon HD 4850
Video Memory 512MB DDR3 VRAM
Graphic Type Dedicated Card

4. iBuyPower Battalion 101 M860TU: 1654.00
Intel® Montevina Core 2 Duo Mobile P8700 Dual-Core Processor (2x 2.53GHz/3MB Cache/1066FSB)
4GB [2GB x 2] 1066MHz DDR3 SDRAM
Mobility DDR3 1GB NVIDIA GTX260 PCI-Express 3D Video
320 GB 7200rpm Serial-ATA-150 Super Slim Notebook Hard Drive
8x Dual Format DVD±R/±RW + 16x CD-R/RW Combo Drive
Vista 32 Bit

5. Dell XPS Configuration: 1899.08
PROCESSOR Intel® CoreTM 2 Duo T9300 (2.5GHz/800Mhz FSB/6MB cache)
OPERATING SYSTEM Genuine Windows Vista® Ultimate Bonus
MEMORY 4GB Shared Dual Channel DDR2 SDRAM at 667MHz
HARD DRIVE Speed: 320GB SATA Hard Drive (7200RPM) with Free Fall Sensor
INTERNAL OPTICAL DRIVE CD / DVD Burner (DVD+/-RW Drive)
VIDEO CARD NVIDIA® SLITM Dual GeForce® 8800M GTX 1GB GDDR3
WIRELESS CARDS Dell Wireless 1395 802.11g Mini Card
SOUND OPTIONS High Definition Audio 2.0

6. Alienware M17 Configuration: 1920.48
Dual 512MB ATI Mobility RadeonTM HD 3870 - CrossFireXTM Enabled!
Intel® CoreTM2 P8600 2.4GHz (3MB Cache, 1066MHz FSB)
17-Inch WideXGA+ 1440 x 900 LCD (720p)
Windows Vista® Home Premium (32-bit Edition) with Service Pack 1
2GB Dual Channel DDR3 SO-DIMM at 1066MHz - 2 x 1024MB
160GB 7,200RPM (8MB Cache) w/ Free Fall Protection

Also:
Regarding the OS - is there any good reason why I should opt for 64-bit Vista over 32-bit? I've only heard 'compatibility issues' this and that. This is probably a stupid question, but will older PC games made in the 98/2000/XP era (like Morrowind) play on Vista?