Hi!
You shouldn't need any converters for those 433's in the BP6. Your 433's are the same more or less as my 300's. They just plug right in and work.
The fastest (non overclocked) celerons the BP6 can run dual is 533's, which are the fastest PPGA celeron's you can buy anyway.
Concerning the "new" FC-PGA celerons, first of all they appear to not be able to run in SMP mode at all, so you can only use one, and you need to use a NEO-S370 adapter to move some pins around for you to use even that one. As far as I can see, the board supports any speed FC-PGA celeron in this config.
The board can also supposedly run a single or dual FC-PGA P3 chips with NEO adapters (I have never tried this). There are some catches though:
1) The P3 must run at 100 MHZ FSB speed (not 133, things go all to hell at 133 MHZ front side bus because the board and chipset were never designed for this speed)
2) P3's must have cB0 stepping or above.
3) For dual P3's you need additional mods, and I believe they must have identical stepping.
As for being current, well, it's as current as your celeron 433's are
That is to say, not very. It's a couple years old. Not many places sell them new anymore. I actually bought mine used (with cpu's) 8 months or so ago (back then you could buy them new very easily though).
Personally I dont think I'd bother trying to get this board to work with anything besides celerons. If I bought a pair of p3 cpu's I'd buy a VP6 or similar to use them in. More of a sure thing.
Hope this helps : )
z