In its latest edition, Consumer Reports has a report on desktops and laptops.
Here's a little rundown:

Reliability
Based on 57,000 laptops purchased between 1999 and 2003. Percentages shown are laptops that ever had a repair or a serious problem.

Apple 17%
Toshiba 18%
Sony 18%
IBM 19%
HP 20%
Dell 21%
Compaq 22%
Gateway 23%

Tech support
Based on "solved problems", "support staff" and "waiting on phone"

Apple 82%
IBM 69%
Gateway 64%
Dell 60%
Toshiba 59%
HP 55%
Sony 52%
Compaq 49%

The ratings

Budget
1. Compaq Presario 2100Z 2500+ Athlon XP-M - $1,000 - Battery Life: 3.5hrs
2. Dell Inspiron 1150 2.6GHz Celeron - $850 - Battery Life: 4.25hrs
3. IBM Thinkpad G40, 2.4GHz Pentium 4 - $1,367 - Battery Life: 3.75hrs
4. HP Pavilion ze5700 2.8GHz Celeron - $974 - Battery Life: 2.25

The Dell Inspiron is the top choice for CR (price/quality).

Workhorse
1. Gateway M350X, 2.8GHz Mobile P4M - $1,500 - Battery Life: 4hrs
2. Compay Presario R3000T 2.8GHz Mobile P4M - $1,574 - Battery Life: 3.75hrs
3. HP Pavilion zx5000 2.8GHz Mobile P4M - $1,424 - Battery Life: 3.75hrs
4. Dell Inspiron 5150 2.8GHz Mobile P4M - $1,576 - Battery Life: 3.5hrs

The HP is the top choice.

Slim and Light
1. Sony Vaio PCG-V505 1.4GHz Pentium M - $1,750 - Battery Life: 4.25hrs
2. Toshiba Portege M205-S810 1.5GHz Pentium M - $2,400 - Battery Life: 4hrs
3. Dell Inspiron 300m 1.2GHz Pentium M - $1,537 - Battery Life: 2.5hrs
4. IBM Thinkpad X31 1.4GHz Pentium M - $2,283 - Battery Life: 4.25hrs

The Sony is the top choice.

5hrs or more is going to be difficult unless you buy a second battery pack... all of these laptops have at least a 40GB hard disk... the only ones less than 6 pounds are the Slim and Light ones.

Hope this helps a little.