Howdy,
I've encountered a problem importing (important) data from a mysql
dump back into mysql.

I did a mysql ( Ver 11.18 Distrib 3.23.54) dump on a RH 7.2 linux box like:
mysqldump db testappdb > testappdb.dump

testappdb.dump is about a gigabyte.

Then I copied testappdb.dump via sftp to a windows 2000 box.

I tried to import the dump file into a mysql 4.0.13
db on the 2k box.

mysql testappdb < testappdb.dump

This process takes a few minutes (1 gig of data). After the import is
complete, sqlyog (a graphical mysql frontend) shows all the tables
imported and of the correct types. The data count for each table also
seems correct. Data_length, Max_data_length etc all seem fine.
However, on querying any table in the testapp db, it returns 0 rows! 
I do not have tools on the 2k box to open and look at the 1 gb dump
file, however it imports via mysql < dump etc with out any errors.

I have successfully imported this same testapp database many times
using this exact method, though with smaller dump files (30 meg
average). The testappdb.dump file on the 2k box is the only record I
have of the data, as the testappdb on the linux server was wiped.

Does anyone have insight as to what is going on, and how I can
successfully import the dump file, or how I can further debug the
problem?

I'd suggest trying to take a look at it with phpmyadmin, or sqlyog as
they are a slight bit friendlier than the command prompt.
The dumpfile is generally a text file, isn't it? it might be worth an
effort to take a text editor and carve out chunks of data to import at
a time.

This may not be the best forum to ask your question, however... A
MySQL specific thread would probably point you quicker to the right
direction.

--
This is a free comment. Backup your data before trying anything
mentioned in this post.