Though I couldn't possibly offer a timeline, these are a few rough estimates of updates to Apple's hardware line (eMac and XServe excluded):
iBook
- 700 & 800MHz G3
- 512K L2 Cache
- 133MHz System Bus
- Mobility Radeon 7500
- 14" Display Still Available, But Fazed Out
iMac
- 867 & 1133MHz G4
- 256K L2 Cache
- 133MHz System Bus
- Radeon 9000
- 15" Education Only, Otherwise 17"
or
- 800MHz & 1GHz G4
- 256K L2 Cache
- 133MHz System Bus
- GeForce4MX 64MB
- 15" LCD low-end, 17" top two
PowerBook
- 867 & 1133MHz G4
- 256K L2 Cache
- 133MHz System Bus
- Radeon Mobility 9000
or
- 733 and 933MHz G4
- 256K L2 Cache
- 133MHz System Bus
- Radeon Mobility 9000
PowerMac
- 1GHz - 1.5GHz Dual G4s
- 512K L2 Cache
- 166MHz System Bus
- Radeon 9700 or GeForce4 Ti 4600
iBook
- 700 & 800MHz G3
- 512K L2 Cache
- 133MHz System Bus
- Mobility Radeon 7500
- 14" Display Still Available, But Fazed Out
iMac
- 867 & 1133MHz G4
- 256K L2 Cache
- 133MHz System Bus
- Radeon 9000
- 15" Education Only, Otherwise 17"
or
- 800MHz & 1GHz G4
- 256K L2 Cache
- 133MHz System Bus
- GeForce4MX 64MB
- 15" LCD low-end, 17" top two
PowerBook
- 867 & 1133MHz G4
- 256K L2 Cache
- 133MHz System Bus
- Radeon Mobility 9000
or
- 733 and 933MHz G4
- 256K L2 Cache
- 133MHz System Bus
- Radeon Mobility 9000
PowerMac
- 1GHz - 1.5GHz Dual G4s
- 512K L2 Cache
- 166MHz System Bus
- Radeon 9700 or GeForce4 Ti 4600