The 4200 RPM drive will be noticeable slower than the 7200 RPM drive of the same size - it will certainly be noticeable.
The Dell XPS 1530 that duckmanbro will certainly work and is a good laptop - I myself have the Dell Inspiron 1520 and have been quite satisfied with it (side note: the 1520 has the 8600M GT DDR2 video card and handles CoD4 well, if not on maximum settings, but somewhat struggles with World of Conflict. The 1530 has the 8600M GT DDR3 video card and thus will do a bit better with both programs).
However, I'd recommend the Sager NP 5792 from powernotebooks.com over the XPS 1530. Here's the configuration you can get for $1968.13:
17-inch 1680x1050 display
GeForce 8700M GT graphics card with 512 MB DDR3 memory
Core 2 Duo T9300 (2.5 GHz) Processor (6 MB L2 cache)
4 GB RAM at 667 MHz
250 GB, 5400 RPM Hard Drive
DVD R-W
Windows XP Professional
The 8700M GT gives a good amount better performance than the 8600M GT. The T9300 also will give a nice boost in performance over the T7500 (2.2 GHz) in the Dell. The hard drive will be a bit slower and have a bit less room, but will still be decently fast - and hard drive speed is irrelevant after loading data. You also get 4 GB RAM, which, though not useful in its entirity without a 64-bit OS, will be useful if you go with a 64-bit OS later. It's only $55 more than 2 GB, so I'd go with it even if you can't use all of it now.
If you prefer a smaller size laptop, the Sager NP 2092 on the same site offers everything the same except the 8600M GT (I think DDR3, not sure though) for $1618.93. Overall it's probably a better deal, but performance is slightly lower.
Slightly less balanced, but the best in terms of pure graphics for under $2000, is the
Gateway P-6831FX from Best Buy:
Genuine Windows Vista® Home Premium (32-bit)
Intel® Core™ 2 Duo Processor T5450 (1.66GHz, 667MHz FSB, 2MB L2 Cache)1
3072MB 667MHz DDR2 SDRAM (1-1024MB & 1-2048 MB module)
250GB 5400rpm Serial ATA hard drive w/ 8MB cache2
17.0" WXGA+ Ultrabright TFT Active Matrix (1440 x 900 max. resolution)
FX Design with Copper Core Accent
Intel® PM965 Chipset and NVIDIA® GeForce® Go 8800GTS with 512MB of GDDR3 discrete video memory
8x Multi-Format Dual Layer DVDRW with DVD-RAM featuring Labelflash™ Technology3
Integrated 1.3 Megapixel Web Cam
The total is $1700 before tax. AFAIK it cannot be bought online, only in the store.
The key here is the graphics card - it is far more powerful than the 8700M GT, and is nearly the fastest mobile card on the market. On the other hand, the processor is by comparison lackluster. So it depends if you're willing to trade longer IBT's in Civ for better graphics in CoD4. Not an easy decision, for sure.
As for mice, listen to what others say. I just use a regular mouse.
