For that reason you mentioned, I ordered cables for my X to take on a trip to Snow Summit up in Big Bear next week. Though I probably won't need them, it would be wise for me to have them.
There is a thread about snow chains, actually cables describing the two types of cables. ZT729 and ZL671. The latter cost a little more but the cheaper of the two uses rubber fasterners which are not advised for the shape of the wheel... Anyway, if you live in the South Bay area, I believe someone posted that Winchester Auto Parts ($78 and $107) has the best price, otherwise online, Howards has them shipped for under $100 and $135 (respectively). Also, within the thread, a couple people make a good argument as to why it would be better to put the cables on the rear vs. the front.