Mr. Olano has provided you with an important link to the Department of State's monthly visa report. Your sister would be in category F4. He is correct in saying that visa numbers for that category are current for priority dates on and before January 1, 2001, unless your sister is from Mexico (in which case, the priority date is March 1, 1995) or Philippines (priority date April 1, 1989). Best of luck!
Look at your I-130 receipt. To the top left there is a box with "priority date." Look at the department of state visa bulletin for the current month. To "adjsut" - become a resident- the I-130 has to be approved (usually within 1 to 2 years) and the "priority date" has to be current. The preference for siblings of US Citizens is the 4th preference with is now in 01/01/01. That means that you have to wait about nine more years. (see this link http://travel.state.gov/visa/bulletin/bulletin_5019.html)