kia ora all - hello from nz

after many many burns my internal cd/dvd writer has called it quits - so i purchased a Macpower peripherals Prefect II cd/dvd external storage enclosure for 5.25" Optical Devices ie external writer.It does not have disc installation for macs- just shows up on screen when you put in cd or dvd

my problem is that while i can burn music cds fine in iTunes i can not burn dvds - it seems that the default setting is 40 MBs so whenever i go to burn movies it says there is not enough space on the disc

so far i have not been able to change this setting - i have been all over my iMac Power PC G5 trying to change this setting and as yet have been unable to

i am sure it is something reasonably simple that i am just not seeing

can anybody help me Please ?? it is really vexing me.I have tried phoning the shop i bought it from but there is a language barrier making it very difficult to explain

any help in getting thedvd writer working properly would be very gratefully accepted

thanks very much

Lee
aotearoha new zealand