Serial port irq conflicts

I have 3 serial ports on the host machine that I need to map to the guest running windows xp 32 bit. I have upgraded to workstation 8 but I am still having irq conflicts. I have added the settings to my vmx file to set the irqs

serial0.present = "TRUE"

serial0.fileName = "COM1"

serial1.present = "TRUE"

serial1.fileName = "COM2"

serial2.present = "TRUE"

serial2.fileName = "COM3"

serial2.irq = "5"

the guest system seems to  ignore these settings and only uses irq 3 and 4. Is there a step I am missing?