The use of importing mass numbers of computers in Deployment Solution can be an incredible time saver for any Altiris Administration team. Altiris has provided, since the 5.5 days, a sample spreadsheet "ImportComputers55.xls" in the Deployment Server\Samples directory to use as a framework when importing computers. Simply enter your relevant data, save as a .csv and import the new computers to DS.
A few known issues have cropped up over the years, and the two available workarounds are provided in the following kb articles:
With the recent updates of 6.9, 6.9SP1, and 6.9SP1 MR1, some people have experienced new issues with this method, that the two previous articles didn't resolve.
.An excellent solution was posted to the legacy Altiris forums, by customer williama (who deserves all the credit).
By adding a blank column in column 4, labeled 'added', the mass import resolves without issue (provided the inputed data is correct).
Please read the post for more details.