My attached screen grab illustrates the problem. Running a sql query brings back columns (called 'start') that show negative numbers, but look in the highlighed metadata portion of the screen grab and you'll see that the 'start' column is defined as UNSIGNED INT. How?
The same query is displayed correctly in Toad for MySQL, the MySQL command line client and the MySQL Query Browser gui tools, so I suggest that this is a real issue with SQuirrel.
If you also do a query to select all the values of the 'start' column that are < 0, nothing is returned, suggesting that the database and sql side of this are working correctly. The problem seems to be with the actual display and rendering of the column's data values.
I'm running MySQL 5.0, java 1.6 and a version 5.x jdbc connector, with SQuirrel 2.6.5a. Hope this helps...