Firewire and external 2.0 same time?

has anyone had this work. instantcopy nero… alcohol… nada … if i mount one inside computer… can do burns to both at same time… but if both are external… no dice… wtf is going on… i have xp pro and 2000 pro

ok after posting…
amd 2000+ 512MB ram abit 333raid motherboard geforce 4600ti 128mb

antec 450w power supply
250 gig hard drive
2(each) sony dru500a
120 gig hard drive
80 gig hard drive
c: (3 gig)

any help would be great. I really wanted two external burners, but only one external and will work. (this strange problem happens on my laptop too) one external firewire, one external 2.0 and the computer freezes when i go to write… I can read from all dvd drives, read medium info… but when I go to press… nothing