There are 2 things that work against a rogue when they first get to Outland.
First is that if you have decent ger for your level in your 50s you can pretty much keep a mob stunned for about 75% of their health. This means the mob only has a few seconds to swing/cast at you before it's dead. Most mobs won't be able to do a whole lot of damage in that time. When you get to Outland the mobs have a lot more HP, and if you aren't in full "Outland gear" you won't have the DPS to take off more than 40-50% of their health in the course of a cheap shot and kidney shot. This means the mobs have a lot more time to hit you, and when they do hit you they do more damage.
The second thing that works against rogues in Outland is that a LOT of mobs there, including ALL of the boars, have a damage shield that does 30-40 damage to you every time you hit them. This isn't that bad if you're a 2h warrior or ret pally swinging 3.5 seconds, but when you're a rogue getting off 1 hit approximately every 1.5 seconds (or less) you end up taking a LOT of damage from the mobs' damage shields.
My advice to you is to go to the AH and look for leather gear, amulets, and rings "of the Bandit". These pieces of gear will give you a huge boost in both attack power and hit points. If you can't find "Bandit" gear, look for "of the Beast". It's not quite as good for rogues as "Bandit", but it's almost definietly better than the Azeroth blues/greens you're wearing now.
Edit: In regards to the 60 PVP stuff, the armor is a complete waste of time. You will get better before you leave HfP. The weapons, however, are some of the highest DPS weapons you will see until you get into the level 70 dungeons. I'm not saying you NEED them, but they are REALLY good weapons for the level. Especially that delicious 2.8(?) speed mainhand slicer.
Edited, May 19th 2008 8:51pm by Bigdaddyjug