How to partition new HD for Linux?

["Andre Fortier" <afortier cse collegeem qc ca>]

I am installing a PC to run Linux. The PC will run only one application,
network monitoring  tool - MRTG, which creates a lot of graphs in
/home/httpd/html. The PC has 2 GB drive. As I am new to Linux I plan to do a
full install (Everything option in install menu) and 2 GB should be enough.
However the Redhat 5.2 Installation Guide (page 55) gives this example of
filesystem configuration which totals to 4 GB:

/ (101mb)
/usr (603mb)
/usr/src (1278mb)
/usr/spool/lpd (509mb)
/usr/local (768 mb)

Could someone explain why those numbers? How many and how big partitions
should I have? Growable or not?

Thanks