I'm not really certain what the question is... How to work with large files?
You need as much RAM as a machine can hold and you can afford. 3GB is scraping the bottom anymore. Especially for large files.
A 64Bit operating system and Photoshop running under 64bit helps.
A separate drive (not partition) to use for scratch space will also help speeds.
A good video card with 1GB of RAM on it. Photoshop utilizes the GPU a great deal anymore.
"Professionals" tend to immediately add RAM to almost every system. An adequate minimum would be about 4GB anymore, but even that can quickly be chewed up.