Can't Shrink The Database Log...

Hi
I have a SQL2k db ABC with only 2mb data but around 500 log. I did the followings
----------------------------------
backup log ABC with truncate_only
dbcc shrinkdatabase(ABC, 10)
Cannot shrink log file 2 (ABC_Log) because all logical log files are in use.
DbId FileId CurrentSize MinimumSize UsedPages EstimatedPages
------ ------ ----------- ----------- ----------- --------------
7 2 58768 128 58768 128

use ABC
sp_spaceused
database_name database_size unallocated space
------------ ------------------ ------------------
ABC 506.75 MB -0.51 MB
reserved data index_size unused
------------------ ------------------ ------------------ ------------------
2248 KB 1288 KB 544 KB 416 KB

sp_helpdb ABC
name size maxsize growth usage
-------------- ------------------ ------------------ ------ ---------
ABC_Data 1728 KB Unlimited 10% data only
ABC_Log 517184 KB Unlimited 10% log only

question:
1. what is the negative -0.51 MB for unallocated space?
2. I can't kill all the process logins, is there other way to shrink the database log side?

thanks
-D