If the mp3's dont have silence on the ends, you can just right click the second track in Nero and set the Pause to 0.
One of the limitations of mp3's is that you'll never get perfect audio on the first and last frames of a file, so if you want a perfect copy you'll need to rip a CD to a single .wav and then use a cue sheet to define the tracks (use EAC). Check out www.r3mix.net for info on that.
If your mp3's have silence on the ends you'd have to edit them, and I know next to nothing about that
Hope this helps.