You can convert it to 24p by putting it into a 24p timeline, selecting "interpolate fields" as your deinterlace method in the project properties, then rendering as 24p DV with 2-3-3-2 pulldown -- then bring the rendered file into your timeline.
Or, if you're using Vegas 6 or later, you can just put it in the timeline with the 24p footage and render it all at once.
Thanks - you are the expert re: 24P ! I was looking more for an VV FX to take the crispness off the 60i footage. . .. .Ill try your suggestion also. . .