Which would be the best choice for gaming?

I'm looking into getting a laptop from alienware or dell to replace my desktop, but I'm not sure if the laptops would be better than my desktop. Here are the specs for my current desktop:

AMD Athlon? 64 FX-53 Processor with HyperTransport Technology
ABIT AV8 - VIA K8T800 Pro Motherboard
2GB Dual Channel DDR PC-3200 SDRAM at 400MHz - 4 x 512MB
ATI RADEON? X800 XT Platinum Edition 256MB DDR3 w/Digital and TV Out
Extreme Performance - Serial ATA RAID 0 - 160GB (80GB x 2) Seagate® Barracuda 7,200 RPM w/16MB Cache

I am looking to upgrading to one of these 2 laptops, so I can take it on the road with me and play more games than I have been. I just wanted to see if anyone here thinks they would be as good as my desktop for f.e.a.r, Half-Life 2, and Call of Duty 2. Also, which of the 2 laptops would be better? Any help would be appreciated:

Alienware Aurora M7700
AMD Athlon 64 X2 4800+ with HyperTransport and Dual Core Technology
17" WideXGA+ 1440 x 900 LCD Display
VIA K8T890 + VT8237A Chipset
2 GB Dual Channel DDR SO-DIMM at 400MHz - 2 x 1024MB
100GB 7200 RPM SATA
256MB NVidia® GeForce? Go 7800 GTX
Price:4500.00

or

Dell XPS M170
Intel® Pentium® M Processor 780 (2.26 GHz/2MB Cache/533MHz FSB)
17 inch UltraSharp? Wide Screen UXGA Display with TrueLife
2GB Dual Channel DDR2 SDRAM at 533MHz 2 Dimm
100GB 7200rpm Hard Drive
256MB NVIDIA® GeForce? Go 7800 GTX
Price:4500


Also, does anyone think that it would be a good computer for the newer games coming out in the future, and is there anyway to upgrade the video cards in laptops? Any help would be appreciated!