Get at least 512RAM. If you can custom order (from Dell HP/Compaq, Toshiba etc. then you can order 256mb and then add your own 512mb RAM stick (only 2 slots in a notebook) for much less.
Pentium M Dothan CPU's (715 or higher) have the best battery life and performance factors right now in a notebook.
Also make sure you get a notebook with dedicated video RAM versus shared or integrated -- it cannot be upgraded on a notebook and shared takes away from your system RAM.
32mb dedicated is fine for general use but 64mb is better (and only 50-75 more on custom models) and some notebooks like the Dell 8600 or Acer have the ATI 9700 video card with 128mb video RAM dedicated.
I am planning to buy a notebook. i would like to load oracle in the notebook. can you suggest good recomendation for the notebook(like RAM size, Harddisk capacity,processor speed).