Flipping computers and memory

I have a MBP 1.1 and its getting old. my mom has a newer mbp from this summer and all she does is use the internet and iphoto. i do alot of cad, sketchup, ps, etc and this one isnt cutting it anymore especially now that cad came out for mac.

i want to put all my info/programs/ etc on hers and put hers on mine.

Will i run into hardware/software issues.

Can this be done easily.

I was thinking
HERS > external hard drive
MINE> HERS
reformat mine and boot from the external harddrive

??

What do you think? any better ideas?