Geez, a lot of misleading advice here. I run 512mb RAM and Illustrator CS2 and Photoshop CS2 run fine together at the same time. I only have a 1.8mhz P4 for my work rig and it runs sweet.

The problem sounds like you need more virtual ram, in XP you can right click on my computer, select properties, advanced tab, performance settings, advanced tab and select change virtual memory. Then alter the size of your virtual memory to suit your requirements. I run with 768mb on each of my 4 hard drives. Which equals 3082mb of virtual RAM and 512mb of ddr2 RAM, total of 3594mb of RAM.