My suggestion are a desktop PC, becouse its a lot easier and cheeper to get a decent desktop then a laptop.
My second suggestion is that you load it with RAM memory, 4 Gb is the lest but i would recomend 8 Gb. We all know that FC love there memleeks...
When it comes to a CPU i would recomend a quad core. 4 cores are always better then 2...
A decent grafikcard are also nice... 512 Mb of RAM or more on it is highly recomended.
Harddrive... Remeber that AoC takes a lot of space... On my harddrive AoC and AO takes about 30 Gb of space together...
OS. I would recomend the 64-bit version of Vista. It have better support for multiple CPU-cores, and if you have more then 4 Gb of RAM you must have a 64-bit OS as a 32-bit OS cant use more then 4 Gb of memory. (2^32 = 4 294 967 296 bit)
If i you have any other questions about other parts, plz write them here and I or anyone of the other "geeks" will try to ansver them...
Here are the specs of my comp... Its a OK gaming computer... The only thing im thinking of changing are the grafikcard. Its a bit slow...
INTEL CORE 2 QUAD Q6600 2.4GHZ 8MB 1066MHZ S-775
ASUS P5K PRO P35 SOCKET 775 ATX
CORSAIR 4GB DDR2 PC6400 XMS2 XTREME (2X2GB) HEATZINK
CORSAIR 4GB DDR2 PC6400 XMS2 XTREME (2X2GB) HEATZINK
ASUS GEFORCE 8600GT 512MB SILENT 2XDVI HDTV PCI-E