The Logic Pro 7 Reference Manual incorrectly states that the Freeze file format can be changed to 16 or 24-bit in Preferences > Audio. This information is no longer true for Logic 7. If you used the Freeze function for exporting audio tracks in Logic 6.x, you can now use Logic Pro 7's much-improved feature, "Export Track as Audio File."

Choose File > Export > Track As Audio File or Export All Tracks As Audio Files.

This opens a file selector that allows you to set the bit depth and audio file format. The first option exports only the selected track, and the second option exports all tracks that actually produce a sound (i.e. which are not muted or only the soloed ones).

This approach has a few advantages:

With the export track function, the tracks are named more conveniently than when using the Freeze function in Logic 6, and you can freely choose the file destination and format for each export.

The Freeze function can only ensure perfect sound quality in all cases when using 32-bit audio. Reading 32-bit files from the hard drive takes only a few percent more hard disk performance than reading 24 or 16-bit files (because most of the time is needed for seeking, not for reading).