Go here, lots of good info and a sister site I believe to this one.
I'm not a computer geek, so my vernacular may be a bit off here. A kernel is the part of a ROM that controls the radio (wifi, processor speed and cell signal). With some customs ROMs, like Ultimate Droid (UD) you can change kernels to speed up the processor of your Droid. Some of them work better than others, and since you say you've rooted your X I assume you have the ability to change kernels.
I found that certain kernels did not allow my wireless tether to work as well as others. Once I found one that worked I stuck with it and no longer had problems tethering my Ipad to my Droid.
Hope this helps,