How to split a field into two fields

I have the following fields in table A:

GL_ID| Date |GL_Name_VC | Amount |Period_TI|Year_SI
================================================== =============
1000|31/12/2005 | Sales | -8,000.00 | 12 | 2005
================================================== =============
1000|06/01/2006 | Sales | -6,000.00 | 01 | 2006
================================================== =============
1000|20/01/2006 | Sales | 2,000.00 | 01 | 2006
================================================== =============
1000|28/01/2006 | Sales | -4,000.00 | 01 | 2006

The above database is running on Microsoft SQL Server 2000 and i would like to query
for a report that looks something as below:

Period|Date |GL_Name_VC| Debit | Credit|Net Change|Balance
============================================== 01 01/01/06|Opening Bal | 0 | 0 | 0 | 8,000
01 06/01/06|Sales | 0 | 6,000| 0 | 0
01 20/01/06|Sales | 2,000 | 0 | 0 | 0
01 28/01/06|Sales | 0 | 4,000| 8,000 |16,000


The formula for the above calculated fields are as below:

Opening Balance = carried forward balance from Year 2005
Debit = All positive amount
Credit = All negative amount
Net Change = Total Credit - Total Debit in Period 01
Balance = Total of Net Change + Opening Bal

Guys, hope someone out there can help me with the sql command for the above report?