you have, like most other people looking for a laptop a real problem in selecting one. Running CFD vs portability. Those two terms aren't very good friends.
For your different things, considering what you like to do here's what I suggest (and trust me, I study computer science):
portable (so long life, lower weight):
- Intel Centrino. You better take a powerful model. The centrino platform is simple the best choice here.
- for longer life you need an onboard graphics card, but for CFD or games that's not really recommended
- without a doubt go for an AMD Ahtlon 64 Mobile. Those are top notch, consume less power, are more powerful and most of the time a little bit cheaper. Intel is simply not in the same league at the moment with the P4.
- as graphics: get a X700(pro) mobile or something
In both cases you should really go for 1GB of RAM, it's not important for your battery life and will greatly enhance performance in everything.
Also, there is almost always onboard sound so you shouldn't worry about that.
HDD: not important for battery life, pick what you want
ps: whatever you do, DO NOY BUY packard bell !