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 scrapping 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.