i think your rep power goes up for every 100 points you get, say if i gave you some now you would get 30, if i where to take some away i would only be able to take half of what i have(15)
You get karma from other members of the forum by doing a good post, telling a good joke, making a good point or by cadging it from your mates (hint, hint.....) You can also get bad karma if someone disagrees with you, you give abuse or make some embarrassing faux pas.
To give karma to a member you click on the scales icon to the top right of their post. You can then choose to give good or bad karma and leave a comment.
You can only give a couple of lots of karma within a 24 hour period. Also you have to 'spread it around a bit' before you give it to the same person twice. To see who gave you karma click on the My Profile option on the toolbar at the top of Accyweb.