I run MxO exclusively on my laptop. I have 1 GB RAM, nVidia FX Go5600 GFX card (8x AGP) and an Intel 4.3-ish GHz HyperThreaded CPU... I think, can't check at the mo. ( with plenty of HDD space )
The top factors affecting game performance are:
GFX card ( This is the biggest factor - unless you have a decent mobile card the game may not run )
RAM
CPU speed
Net connection speed
I would recommend setting your in-game GFX settings to lowest and turning off ped/car activity.
Also, external to the game, in windows display settings > Advanced make sure that your laptop has all battery saving optimisations turned off as they will seriously affect your GFX performance.
Make sure that your CPU is set to performance mode ( if you have CPU optimisation software running as most Toshiba / IBM / Sony laptops have by default ).
Kill off any filesharing or P2P software you may have running as well as any excess programs ( like VoIP programs such Skype or others like Quicktime ) running in your system tray ( the bit on your task bar next to the system clock ).
Run the game ONLY when plugged into the power adapter for the laptop ( this will make sure that any other automated power saving / performance killing settings are turned off by the hardware )
There are a few extra optimisations to do but they won't make too much difference.
I'll update this tomorrow ( it's 12:51am and I'm going to bed ). Best of luck.
Make sure when you install to the laptop that you copy your current PC MxO install director over to the laptop afterwards ( see my sticky thread "Backup... It's what's for breakfast" ) otherwise you will spend the trip patching rather than playing

Message Edited by phi on 03-06-200611:55 PM