Dano,
There are two ways : either buy a Toshiba, or possibly other type, laptop with a docking station that includes a PCI slot into which you can fit an Appian multi-monitor card (or similar). This is possibly the best desktop solution, ie. if you do not intend to transport your monitors. If this is the way you go, take extra advice from the manufacturer re the docking station & Appian to ensure that the card will fit & work. I have found Appian tech support to be very helpful, although I did not take the above route as I wanted a truly portable trading station.
Just under a year ago, I bought a Compaq Presario 1800T 850mhz 20gig 320ram W2000 laptop with 15" 1600x1200 res screen. I bought it for the screen resolution (fabulous, although you have to adjust the Windows settings to make the font size bigger for easy reading) and because I was assured by Compaq that, like Toshiba, there was built in support to plug in an external monitor as a true desktop extension (rather than just as a mirror image of my laptop screen). Unfortunately, Compaq turned out to be wrong on the second point & I did not discover this for several months, by which time I was out of the USA.
Had my laptop beeen able to drive an external monitor as I had intended, the three monitor workstation solution would have been as follows : connect one monitor directly to the laptop 'monitor out' (RGB plug, I think - an analog connection). Buy an Appian Traveler PCMCIA card, into which plugs monitor #2 (digital or analog, 1280 x 1024 max resolution). Then the Appian Hydravision software that comes with the PCMCIA card controls the lot, along with W2000 (essential, btw. Don't have any experience of Windows XP). Et voila !
For anyone interested, I have ended up with an excellent, truly portable workstation : I now have an Appian Traveler PCMCIA card, into which I connect a Sony M61 16" lcd, the smallest lcd with 1280x1024 resolution (much less bulky that a 17" lcd) - much better (although twice the price of) a 15" monitor. It fits upside down into the document pocket of my laptop briefcase, although the briefcase ends up weighing over 10kg, which can cause check-in problems with strict European check-in operators (the solutiion here is to either have a friend hold onto the monitor while checking in, or check the briefcase into left luggage for 15 mins while checking in, then reclaim ... no problems using this regrettably devious approach). The good news is that I could never have travelled with 2 external monitors anyway - much too bulky.
Hope that helps !