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Height and Weight data is stored in appearance.dbf. What you need to do first is find the PLAYERID of the player you want to edit in players.dbf; search by first name or last name (last name is probably easier) to find the player you want to change and make a note of their PLAYERID. Note that some players appear multiple times in the database because they appear on All-Star teams in addition to their NBA team. It's probably a good idea to keep searching for the player until you've found all their entries and noted each ID number.
Now you can open appearance.dbf. Search for the number(s) you've written down, this time in the APPEARID column. This will locate the entry that corresponds to the players.dbf entry. You'll see a HEIGHT and WEIGHT column. HEIGHT is in inches, WEIGHT is in pounds. WEIGHT is therefore easy enough to change but HEIGHT will require a calculation. It's probably easiest if you remember that 6'6" is 78 inches (a value of 78 in the HEIGHT column), so you can add or subtract inches as necessary to get the right value. 6'10" becomes 82, 6'3" becomes 75, and so on.
When you edit values in DB Commander, simply move to another cell (box) in the database. The changes will be saved automatically. When you're done, close DB Commander, run NBA Live 06 and re-load the saved file (this is why you always work with files in the saves folder). You should now see the changes in-game. Remember that it's important that you close DB Commander or at least log out any databases you have open before trying to load the rosters in-game, otherwise you won't see the changes.
Hope this helps!