Need help buying a new laptop

I'm a Graphic Designer. I work from home. My current computer is a G5 tower (Dual 2.5 w/ 8GB Ram). So what I want to do is get a MBP for my new setup so I can ad some versatility to my situation. I can use it as a second station in my other room (working from home in one room is boring), and have the ability to me mobile (work from a cafe, extended vacation, etc).

my concern is whether a MBP will do the trick for what I do, and which one. I'm feeling the 17" is too bulky for travel, so I'm thinking the 15" 2.66. and I can hook up a second monitor for my tools (any small light monitors out there good for this? I'd like it low so it matches the height of the laptop screen).

I'm worried about ram (4GB only), but I heard you can max at 6 or 8. is this true? which models can you do this with and how much?

also, will it be impractical to work long hours on a laptop?

my other option is to chuck the MBP idea and get a new Mac Pro, since my current tower is aging by the day.

any info would be appreciated, whether technical, advice, insight from working similarly, etc.

thanks all!

I have the previous MBP 15" (mid-2008) and bought it for video production/editing. At the most, I've had iTunes, Final Cut Express, and Safari open and running simultaneously and haven't experienced any lags. Personally, I've probably only worked for no more than 4 hrs straight at a time and it does heat up, but has never overheated and shut down/went to sleep. That's the closest I can say I've come to the conditions you're describing.
I'm sure the new unibodies perform even better. Especially if you go with 4gb RAM (I'm currently stocked with 2gb). Don't know how well they handle 8gb - only what I've read on other threads in here.

Here's my specs to compare with a newer model:

Model Name: MacBook Pro
Model Identifier: MacBookPro4,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.4 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 3 MB
Memory: 2 GB
Bus Speed: 800 MHz
Chipset Model: GeForce 8600M GT
Type: Display
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 256 MB
Color LCD:
Resolution: 1440 x 900
Depth: 32-Bit Color

4GB of RAM is more than enough to have all the Adobe suites open at the same time with Firefox open and not lag.

I'm doing this on a MB too.

i have and older macbook core 2 duo 2.0 with 4gb ram and do not see any lag. it is used for presentation with propresenter with many windows opened (i like to open webpages and leave it and work in a new window or tab). i do get an overheating issue, but that is only because of a missing heatsink screw. you should be fine with a macbook pro 15 inch.