Comparing Dell XPS XPS M1710 (17 " Widescreen) with ThinkPad T61 1(5" Widescreen)

I have customized a Dell system and a thinkpad for XP Pro. At Dell, on
M1710 (17 " Widescreen) has XP Pero option available. I prefer 15". I
tried to bild tehe two systems w/ the same component

DELL XPS M1710 (17 " Widescreen): $2,633
Intel® Core™ 2 Duo T7200 (2.00GHz, 4MB L2 Cache, 667 MHz FSB) -
(Note: I didn't opted for T7500 for price issues)
Genuine Windows® XP Professional
2GB DDR2 SDRAM at 667MHZ, 2 DIMM
160GB SATA Hard Drive (5400RPM)
8X CD/DVD Burner (DVD+/-RW) with double-layer DVD+R write capability
256MB NVIDIA® GeForce™ 7900 GS - (Note: No 8000 Series available)
Intel PRO/Wireless 3945a/g - Note: This is the only option available
Dell Wireless 355 Bluetooth Internal (2.0 + Enhanced Data Rate)
80 WHr 9-cell Lithium Ion Primary Battery
Integrated Sound Blaster® Audigy™ HD Software Edition - Note: Only
$25 less for integrated audio
McAfee SecurityCenter with anti-virus, anti-spyware, firewall, 15-
months - Note: It comes with it; cannot remove
Microsoft Works 8 - Note: I don't care about this
Yahoo! Music Jukebox - Music Player - Note: I don't care about this
but FREE
1Yr In-Home Service, Parts + Labor,24x7 Phone Support
and ..
LCD PANEL 17 inch UltraSharpâ„¢ Wide Screen UXGA Display with
TrueLifeâ„¢
Network Card and Modem Integrated 10/100/1000 Network Card and Modem
Adobe Software Adobe® Acrobat® Reader 7.0
Miscellaneous Award Winning Service, Support
XPS Specialized Support Inspiron XPS, Specialized Support
Labels Windows XPâ„¢
Processor Branding Intel Centrino Core Duo Processor



ThinkPad T61 (15" Widescreen): $1,588.50 saving $529.50 if buy today
Intel Core 2 Duo T7500 (2.2GHz 800MHz 4MBL2)
Genuine Windows XP Professional
15.4 WSXGA+ TFT
NVIDIA Quadro FX 570M (256MB Open GL) - (Note: No other option
available)
2 GB PC2-5300 DDR2 SDRAM 667MHz SODIMM Memory (2 DIMM)
UltraNav (TrackPoint and TouchPad)
160GB Hard Disk Drive, 5400rpm
DVD Recordable 8x Max Dual Layer, Ultrabay Slim
Intel Wireless WiFi Link 4965AGN - (Note: I like this option better
than Intel PRO/Wireless 3945a/g)
Integrated Bluetooth PAN
9 cell Li-Ion Battery
Express - 1 Yr Depot Warranty

Questions:
1. Is the price difference mainly from NVIDIA Quadro FX 570M (256MB
Open GL) versus 256MB NVIDIA® GeForce™ 7900 GS + the 17" Widescreen
versus 15" Widesceen monitor
2. Replacing the wireless card to desired one wouldn't be a big deal
in Dell, right?
3. Upgrading Memory in Dell could be expensive, right? Only Dell
brand can be used and must be purchased from Dell, right?

At http://www.nvidia.com/page/quadrofx_go.html is info on NVIDIA
Quadro FX 570M
At http://www.nvidia.com/page/geforce_7900.html is info on 256MB
NVIDIA® GeForce™ 7900 GS

Since I really prefer 15" screen, I guess I have to settle with NVIDIA
Quadro FX 570M (256MB Open GL) . Is that justifible? Will I regret
later?