This is for SQL Server 7.0, but should get you started.
SELECT so.name as Table_Name, sc.name as Col_Name, st.name as DataType, sc.prec, sc.scale, sc.isnullable
FROM sysobjects so, syscolumns sc, systypes st
WHERE so.type = 'u'
and so.id = sc.id
and sc.usertype = st.usertype
ORDER BY so.Name, sc.colorder