Go with the Socket 370 FCPGA board. Slot 1 and Socket 370 are both "sockets" that accept CPU's. FCPGA, PPGA, and SECC, SECC2, and SEP are all CPU form factors (the actual layout of the processor). FCPGA and PPGA both use Socket 370, though there are some differences to note (see below), while all SECC, SECC2, and SEP (cartridge style) processors use Slot 1.
A Socket 370 FCPGA board should be able to take any FCPGA PIII, PPGA Celeron, or FCPGA Celeron II. It will not take SECC, SEP, or SECC2 cartridge style processors (which are being phased out anyway).
A Socket 370 PPGA board will take a PPGA Celeron and that's about it. It will not take cartridge processors nor will it take an FCPGA PIII or FCPGA Celeron II without an adapter (of which only ONE exists and it's not that great).
A SLOT 1 board will take Celeron/PII/PIII SECC, SEP, and SECC2 cartridges, as well as FCPGA and PPGA Celeron/CeleronII/PIII processors via an adapter (FCPGA or PPGA to Slot1 adapters are widely accepted and used).
So it almost seems as though SLOT1 is the best way to go...however, SLOT1 boards are becoming few and far between as are cartridge style processors. Therefore, Socket 370 (FCPGA) boards are really the way to go if you're planning on keeping your system upgradable for some time.
(P.S. the main *visible* difference between FCPGA and PPGA is that the core of an FCPGA processor is on top of the chip instead of underneath...hence "FC" stands for "Flip Chip"...this allows for greater heat dissipation)
(P.S. II, if you look into starting with a Celeron, go with a Celeron II (any Celeron 533Mhz or better). The newer celerons are based on coppermine technology while older celerons are basically crippled PII's)
Slackmaster 2000