the max ram for the dell is 320mb
Are you sure that's the max?
That means you must have something along the lines of this configuration for memory:
3x128mb = 384mb
1x256+1x128 = 384mb
It's most likely the second setup, as I believe most notebook/laptops only have two memory slots. I'm guessing you should be able to at least switch out that one stick of 128mb of memory for a 256mb stick for a total of 512mb (448mb including shared VRAM)
Either way, 64mb of your memory is being used as video memory (384mb - 64mb = 320mb).
Windows XP uses about 300mb of memory, so that only leaves about 20mb of memory for your computer to use.
That's not a lot ...