If you search the forums at the site in the link above this message, you will see that "safe" is probably not something you should expect from this mod. You probably stand a decent chance of ruining your ATA 100 card and, even if the mod goes successfully, there are performance issues using some Maxtor drives in a RAID configuration.
The benefits and geekiness of having RAID, however, seem worth the risk to me. I am planning to try to modify my Maxtor ATA 100 card soon and hook up two Maxtor drives for RAID 0. I'll post my results afterward...