Assuming that your final output is a 16:9 television, then place your 4:3 clip on the timeline, then right-click the clip and select 'media source options'. From the drop down list select 'Keep Aspect Ratio - no letterbox' and click OK. You can see the effect of this (and the other media source options) in the Preview Window, although I prefer to preview these on the camcorder itself as the black bars are evident.
If your final output is a 4:3 television and you want the black bars on 4:3 clip then your only option is to place a solid black colour on tracks V1 and V2 and use a moving path to position them.
Post back and let us know jow you get on!
COMPAQ something or other with 500Gb Boot Disk, 1Tb external Firewire Disk, 4Gb Memory and a super duper sound card, 19" TFT Monitor etc etc etc
Sony TRV33e : Sony TRV310e : Canon XM2
Sony Vegas Studio editions to v11
Remember, there is always more to learn than there is to teach.