You were asking about flip chips:
The FC-PGA format is the newer format where the CPU is bare and not encased in one of those black plastic cartridges (SECC for Slot1 boards). The bare chip fits directly into the Socket 370 socket on any Intel 815E based mobo. I believe that all the Celeron II's come only in this format. The flip chip is the way to go 'cause it's more versatile - it'll fit a Sockec 370 mobo directly or a Slot 1 board with a 'slocket' adapter.
But, I think that instead you should get a Pentium III Coppermine in the FC-PGA format and from the recent cB0 stepping. You can get a 600E or a 650 for about the same as the Cele you're looking at if you shop around. And when overclocked the Coppermine, especially a cB0, will outperform the overclocked Cele. Cele fans get mezmerized by the overclocked MHz and neglect to look at the benchmark results. The Cele was the way to go once a while back, but its hayday has past. It just takes people a while to realize it (or admit it). You have a nice up to date board there - get a CPU to match.
If you only have a $100 to spend on the CPU, then get a Cele II. But if you can go $200 - $250, then go Coppermine. And why change from a 566 to a 600 - that doesn't sound smart to me at all. The difference is insignificant.
AnandTech tests have shown that a Cele II 566 at 850/100 is bested by a stock P3 600E at 600/100 in most benchmarks !!
