Quacka: There is a notorious WinXP secuirity update which really messes up burning on a lot of systems, it is security update 811493. If you have installed this update, try uninstalling it.
More likely, you are getting hit with the same problem that countless others suffer from including myself. It's bug in Nero I believe, but Ahead has so far failed to discover what causes it. Unfortunatly, I have no solution for you in this case. Every once and a while Nero will let me burn at full speed properly, other times, I'm stuck between 12x and 24x depending on how the software is feeling. Oddly enough, I find that running programs in the background actually HELPS nero read from the HDD faster! I usually run Kazaa Lite When burning, and just set up a download or two of something, it doesn't matter. The trick is to keep the HDD accessing, without bogging down your I/O channel too much.
by the way, I've noticed other software does not suffer from this problem, or at least alcohol 120% doesn't. So you wan always use WinISO to make an image, and burn it using Alcohol 120% and see how that works for you.
Punch Cards -> Paper Tape -> Tape Drive -> 8" Floppy Diskette -> 5 1/4" Floppy Diskette -> 3 1/2" "Flippy" Diskette -> CD-R -> DVD±R -> BD-R
The Progression of Computer Media