are you getting the darwin bootloader? (press any key to boot from DVD)

if not you need to either:
go into your bios and configure to boot by default from the CD if inserted,
or if your computer has it, go to the bootmenu and boot from your CD.. i use ESC at my HP blue screen..

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MOBO: HP M8100n AMD Media Center TV PC
OS: 10.5.8 (Updated from iPC OSX86)
Kernel: 9.8.0 Voodoo Kernel
Processor: Athlon 64 X2 with Dual Core technology
MotherBoard: MCP61
Graphics: nVidia 9600gt 512 mb
Audio: Realtek ALC888: Digital Output
Chipset: Apple nForce ATA
Ethernet: MCP61 LAN (Realtek RTL8201N)