You can indeed script out passwords from sql server 2000 and import them into sql server 2008 so that they are recognised as upper case passwords. Here's some background reading that will be useful in understanding sql server password hashes, so you can following along with the example.
SQL Server 2000 passwords were actually case insensitive as described in this rant.
Even so, the sql server hashes store a case sensitive and case insensitive copy of the password, so that when you migrate password hashes to sql server 2005/2008 your passwords are then case sensitive.
To test this out, you can run the following on your SQL Server 2000 Server:
exec sp_addlogin @loginame= 'usera' , @passwd='password'
logging into SQL Server 2000 as usera works with 'PASSWORD' , even though it shouldn't. To migrate usera to SQL Server 2005/2008 we can use the following to copy the login keeping the sid & password hash:
'exec sp_addlogin @loginame ='''
+ [name] + ''''
+ ', @passwd= '
+ ', @sid= '
+ ', @encryptopt = ''skip_encryption_old'''
from sysxlogins where name='usera'
You will get the following output (with different sid & hash of course):
exec sp_addlogin @loginame ='usera',
@sid= 0x06cf56eb108a12428712f8b7c66ca1cd, @encryptopt = 'skip_encryption_old'
What you can do is perform some 'processing' on the password hash before importing it into 2008 so that the second upper case hash overwrites the case sensitive hash. This will mean all your passwords are in upper case. Using the password has above, you can perform the following operation, which I've done here in t-sql:
declare @old_passwd char(94) -- original hash from sql server 2000
declare @new_passwd char(94) -- new upper case password for sql server 2008
declare @cs_hash char(40) -- case sentive part
declare @ci_hash char(40) -- case insentive part
declare @salt char(14)
set @old_passwd = '0x01004409EB54922C0CD2BEDBAD754F37AFAD4053BDADF719FF80C8A8ABF5801B813114BE6BA0C2C8543B2DB77B33'
set @salt = SUBSTRING(@old_passwd,1,14)
set @cs_hash = SUBSTRING(@old_passwd,15,40) -- not used, but here for understanding
set @ci_hash = SUBSTRING(@old_passwd,55,40)
set @new_passwd = @salt + @ci_hash + @ci_hash
using this @new_password as the @passwd parameter for sp_addlogin will mean the password is recognised as upper case!