You can follow that generic example in Premiere, I just followed it in Premiere Elements 2.0, as I thought that would be more similar to Prem' Pro 1.5 than the 6.0 version I usually use.
1: Premiere allows more than 1 video track.
2: file > export > frame
3: open the frame in an image editing app' like photoshop or even MS Paint for this stage.
4: double click in the relevant bin > select your edited frame > drag onto video layer above the one you want to censor on the timeline
5: video effects > keying > chroma key (select black as the colour)
6: drag edges of the imprted image clip to cover relevant area of the timeline
7: video effects > stylize > mosaic (fiddle with settings until happy)
8: in clip properties box expand motion > click on the little stop-watch icon to activate key-frames, adjust values along the timeline so the censored layer remains over the right area.
Obviously you could change this, I did it quickly following that generic guide, you could use a blur effect and a luma matte instead, or you could search your help for Track Matte and do it like that instead.
Panasonic SD9, Panasonic NVGS-75, Canon MV600i