Yeah, they're the same thing, just different heatsinks. As far as I know, both of them use Micron D9 chips, so they overclock the same too.
G.Skill 2GB DDR2-800 HZs are better than the XMS, but they're out of stock. Those overclock better, and are more stable. Not saying the XMS is bad in any way, the G.Skill HZs and the XMS are both overclocking favorites. The G.Skill's just known to overclock farther (DDR2-1066 isn't uncommon).