This one is free and designed around what you intend to do
http://www.videohelp.com/tools/Mpg2Cut2 I haven't used it, so your mileage may vary
EDIT:
Homepage for the tool:
http://rocketjet4.tripod.com/Mpg2Cut2.htm
Direct Rapidshare Link:
http://rapidshare.com/files/254078521/Mpg2Cut2_9710.zip
EDIT 2:
Here's another called 'Cutterman'
http://www.videohelp.com/tools/Cuttermaran