Just wondernig as my CD-ROM can burn at 40X, media is 52X rated, but CD only burns at 24X or so.

yes, but not usually. write speed is usually limited to media type, quality, etc... 52X, 40X, refers to READ speed, not write speed.

Write speed is almost always slower.

The motherboard cannot inherently limit the write speed of an optical drive.

The only possible scenario in which that could occur is if, via hardware or software, the optical drive has been put into PIO mode. In that case, there is a much higher load on the system to do any sort of access on the media. Windows XP has a habit of enabling PIO mode for arbitrary reasons, but usually you'd notice pretty quickly that it was acting up.

If you have a burner that can write at 40x, keep in mind that this is only the peak speed at which the unit can burn, and only then towards the very end of the disc. Unlike hard drives, CDs write from the inside out. Burn a full CD, and watch the speed in real-time. You'll see it start out slower and pick up as time goes on.

Lower-quality media has a lower chance of being able to burn successfully at higher speeds. Usually, your drive will attempt to autodetect the speeds the media can be burned properly at. Often, the application you are using will have a function to force the write speed higher, but even that cannot surpass the inherent limitation of optical media. That is, the closer you are to the center of the disc the faster it must spin to maintain a particular speed.

Try other media first.

Now where have I heard....

"The sun is the same, in a relative way, but you're older...
... shorter of breath, and one day closer to death."

Now that's a perfect burn irregardless of speed.