"Frame size: 1024 x 768"

Bingo!

AVI can only render in traditional "video" sizes - 720x480 for NTSC and 720x576 for PAL, or flavors of HD (1280x720, 1440x1080 1.33 stretched pixels, and 1920x1080). I don't exactly recall, but you MIGHT be able to render smaller like 360x240...?

They should have some form of drop-down menu of standard sizes you can pick from - don't stray outside the numbers.

Try Quicktime - the Animation Codec set to 100% is uncompressed, and to tell you the truth, I can't really tell the difference between 100 and 75% if you want a smaller file size. But if it's going to go to something like After Effects, played with, then re-rendered out, or part of an overall animation you will be editing together, then you really should set it to 100% - otherwise you may start to run into something akin to a Xerox of a Xerox - does that make sense?

QT can also do "odd sizing" so your 1024x768 would render out just fine. This is also why you find renders at VERY odd sizes just for FX elements - a 150 wide by 1200 tall animation of rising steam with an alpha - get it?

If you're editing these together, you would bring them into something like Adobe Premiere, or Apple Final Cut Pro, Sony Vegas, Pinnacle Studio, AVID (they have a bunch, really...), and when you've edited your clips to form the complete movie, you render out whatever format you want from THERE - QT, AVI, MXF, etc.

I hope this helps-

-Lew