Re: Different aspect ratios in the same sequence?

Look at the pixel aspect column in final cut for your clips and sequences. Your sequence settings will also tell you your aspect ratio.

Two basic rules:
1) NTSC/PAL SD video is rectangular whether it is 4x3 or 16x9.

2) 1280x720 & 1920x1080 are square. Other flavors of HD are most likely square-but it depends on the format.

I wouldn't recommend blowing up SD video in a HD timeline via Final Cut scaling/distort. There is a really good plugin for After Effects called Magic Bullet Instant HD which in my opinion does a really good job of converting SD to HD.