what is the FSB of a socket 478 pentium 4? what memory is best with it? (considering the 1:1 rule)

Argue for your limitations and sure enough, they're yours.

S478 can be 400 (100MHz), 533 (133MHz), or 800 (200MHz). The 1:1 rule applies to bandwidth.

Bandwidth = "effective" FSB x 8

At 800FSB, the bandwidth is 6400MB/sec (800 x 8), so to have a 1:1 bandwidth ratio with the RAM, you should have 2 sticks of PC3200 running in dual channel mode @ 200MHz.

Remember that DDR-SDRAM is named for the amount of bandwidth (aka throughput it can handle), so PC3200 can handle 3200MB/sec...in dual channel mode (x 2) you have 6400MB/sec

ASUS A7N8X-X
Athlon XP 1800+
8.5 x 200MHz
1024MB PC3200 2.5-3-3-7
Asus A9550GE/TD 128MB
WinME/WinXP Pro SP1

If you want more accurate info you need to tell which CPU you have exactly because there are different models of them. At some speeds they even come with two different FSB clocks!