I am running C3D on two different laptops both with good results. The first is a two year old Dell Covet (2.8Ghz dual core, 8GB ram, 1GB FX3500 graphics card, twin 7200 rpm sata drives in raid0) originally 64bit XP, now dual boot XP and 7. I'm also running C3D on a MacBook Pro with i7 processor (dual core, 2.8Ghz, 8GB ram, 512MB NVIDIA card, 7200 rpm sata, no raid) with Parallels 6.0, 64bit Windows 7 VM. As mentioned both computers do quite well. The Dell has an edge on graphics and speed, which would be expected (compared to a VM) I suspect the drive speed (absence of raid) is a bottleneck with the Mac. I do prefer to travel with the mac, mainly because the 200 watt power supply for the Dell weighs roughly the same as the combined weight of the mac and mac power supply. Some day when the Dell is no longer needed, I plan to use its power supply as an extra boat anchor. The previous recommendation for solid state drives is sage advice. I would have put one on the mac, (had the mac purchase not been an experiment). Now that it is proven, I will eventually install a SSD.
Both computers have high resolution screens, however I use large external monitors in the office for each machine. My recommendation on selecting screen size and resolution should be based on how mobile you are, and how available external monitors are at the office, field office, flat panel tv in the hotel room etc. If you are going to use the laptop regularly in single screen mode, the 17" with 1900x1200 (which was previously recommended) will be the best. Occationaly I travel with both the 17" Dell and 15.4" Mac. The bag that I need to use to lug them around requires that I leave my man-card at home ;).
One last thing to point out on the 17", the only way to comfortably get any work done on a flight, is from the first class cabin. Most of the business or economy class seat spacing make it futile to work with that big of a laptop.
Richard Sincovec:Richard has some great advise here.
I'd recommend Xi Computers or Sager Notebooks.
Keep in mind that C3D is a single-threaded app, so best bet is to get a very fast CPU. Many cores are not necessary. One of the new 2nd Gen i3/i5 chips is ideal. Get Win 7 x64 as the OS (this is very important). You may also want to go the SSD route - it can give a nice boost to performance. But if so, keep in mind that Win 7 x64 can really eat hard drive space, so I'd recommend 120GB minimum.
It is recommended that you get a display capable of 1920x1080 resolution, with 17" minimum size. You don't need a Quadro or FireGL, but you also don't want a bare-bones card or business-oriented card like the Nvidia NVS series. The GeForce 400-series works well.