Audio Codec difference preventing joining files

[LPS-Au]

I want to join two files to create one film on DVD (part of the one program recorded by two different machines). However, when I try to join I get the following message:-

Current joiner uses audio codec: MPEG and a sample rate: 48000.
Video being added has an audio codec: AC3 and a sample rate: 48000.
Audio parameters must be the same when joining.

How can I change one of the codecs and which should I do the AC3 is on a file that is only about 2% of the full film.

Thanks for your assistance.
Peter S.

[phd]

In the file save dialog box, click the Options button and choose MPEG audio.

[LPS-Au]

Thanks for your help Pat, have tried and it has worked a treat.
In the past I have only dealt with one source file so the defaults (whatever format they were took care of themselves).
In this case I recorded the major portion of the program on the PC, but because my Nero 7 takes some time to program, I used a VCR to record the start of the program and then attempt to join the two parts together.
Actualy I am not very happy with Nero at present I find that it causes the software then the PC to lockup and needs to be rebooted.
Thanks again for your speedy reply.
Cheers and a Happy New Year, Peter Stacey.