The processor is the laptop's engine. More megahertz means faster programs with fewer crashes or freezes. Figure that 650MHz is relatively fast and 400MHz is a good mid-level. Don't get less than 200MHz. RAM is your laptop's short-term memory.
Web browsers tend to hog it.
The more megabytes, the better. A larger screen costs more but makes it easier to use for Web surfing and more visual programs. The smallest screen available is 11 in., and the largest is 15 in. The Pentium III is the fastest Intel chip. Steer clear of anything advertising less than 2.5 hrs.