delete command

From: ST (ST_at_discussions.microsoft.com)
Date: 01/09/05 

Date: Sun, 9 Jan 2005 11:13:01 -0800

I have a table that lists multiple records for 1 subject. I'd like to delete
all extra records except the first one listed...is there a way to do this?

example:

PID SID BID
1 5 14
2 5 15
3 5 16
4 6 25
5 6 26
6 7 30
7 7 31
8 7 32

I would like to keep the first one listed for that SID. So, keep PID 1, and
delete rows PID 2 and 3...keep PID 4, and delete PID 5, keep PID 6, and
delete PID 7 and 8. is there a way to do this? Thanks!