You don't want to use expansion bolts, because the length of the bolt coming out the back of the hold varies. If there isn't enough the bolt won't expand enough, so it can pull out the wall.
You're better of using resin in anchors, they're miles better and alot cheaper.
Use the 80mm ones...
http://www.hilti.co.uk/holuk/modules/prcat/prca_navigation.jsp?OID=-37893
You'll need the right resin for the type of brick/stone wall
http://www.hilti.co.uk/holuk/modules/prcat/prca_navigation.jsp?OID=-27372
Rawplug do a version too.
But you are better off building a wooden wall, that way you're not peppering the wall with loads of holes, so your folks won't moan as much.
Show them this and tell them you want to build one in your room.
http://www.facebook.com/photo.php?pid=2025945&id=32465140965
http://www.facebook.com/photo.php?pid=2025946&id=32465140965