really strange...the shell command cpu tells me that there are 2 CPUs:
System: PowerMac3,5
Machine: 0x1
PageSize: 4096 Bytes
CPUCount: 2
CPU0: 7445/7455 (G4) Version 32769 Revision 771
CPU0: CPUClock 599999998 BusClock 133160004
CPU0: FPU Unit exists
CPU0: Altivec Unit exists
CPU0: Performance Monitor Unit exists
CPU0: DataStream Unit exists
CPU0: ReservationSize 32
CPU0: Ticks 4
CPU0: CacheL1Type 0x0
CPU0: CacheL1Flags 0x1000F
CPU0: ICacheL1Size 32768
CPU0: ICacheL1Lines 1024
CPU0: ICacheL1LineSize 32
CPU0: DCacheL1Size 32768
CPU0: DCacheL1Lines 1024
CPU0: DCacheL1LineSize 32
CPU0: CacheL2Type 0x0
CPU0: CacheL2Flags 0x1001D
CPU0: ICacheL2Size 262144
CPU0: ICacheL2Lines 0
CPU0: ICacheL2LineSize 0
CPU0: DCacheL2Size 262144
CPU0: DCacheL2Lines 0
CPU0: DCacheL2LineSize 0
CPU0: CacheL3Type 0x0
CPU0: CacheL3Flags 0x1001D
CPU0: ICacheL3Size 2097152
CPU0: ICacheL3Lines 0
CPU0: ICacheL3LineSize 0
CPU0: DCacheL3Size 2097152
CPU0: DCacheL3Lines 0
CPU0: DCacheL3LineSize 0
CPU1: 7445/7455 (G4) Version 32769 Revision 771
CPU1: CPUClock 599999998 BusClock 133160004
CPU1: FPU Unit exists
CPU1: Altivec Unit exists
CPU1: Performance Monitor Unit exists
CPU1: DataStream Unit exists
CPU1: ReservationSize 32
CPU1: Ticks 4
CPU1: CacheL1Type 0x0
CPU1: CacheL1Flags 0x1000F
CPU1: ICacheL1Size 32768
CPU1: ICacheL1Lines 1024
CPU1: ICacheL1LineSize 32
CPU1: DCacheL1Size 32768
CPU1: DCacheL1Lines 1024
CPU1: DCacheL1LineSize 32
CPU1: CacheL2Type 0x0
CPU1: CacheL2Flags 0x1001D
CPU1: ICacheL2Size 262144
CPU1: ICacheL2Lines 0
CPU1: ICacheL2LineSize 0
CPU1: DCacheL2Size 262144
CPU1: DCacheL2Lines 0
CPU1: DCacheL2LineSize 0
CPU1: CacheL3Type 0x0
CPU1: CacheL3Flags 0x1001D
CPU1: ICacheL3Size 2097152
CPU1: ICacheL3Lines 0
CPU1: ICacheL3LineSize 0
CPU1: DCacheL3Size 2097152
CPU1: DCacheL3Lines 0
CPU1: DCacheL3LineSize 0
System:>

But still it reports 600Mhz