Preserving Timestamp Information

How can I preserve timestamp for a set of data? I'm using PostgreSQL
8.02. I had to do a dump of my database and then at a later date I
imported the data I had in several tables. Here's an example:

yw_id weight yarnweight_lud
--
1 Cobweb 2005-01-13 15:21:50.654149
2 Lace Weight 2005-01-13 15:21:50.654149
3 Sock 2005-01-13 15:21:50.654149

When I use the import wizard for Aqua Data Studio, it sets all values
for yarnweight_lud to NULL.

I can create insert queries for all of these if I have to but I need to
know how to force preservation of the time stamp.

--
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