I have found it very difficult to find "acceptable" stock images from my previous images.
The first issue is image quality my previous camera was a Canon Powershot s80. And while the images are very nice when blown up to 8x10, you can definitely see a difference in quality between the rebel Xti even with the kit lens.
The second issue is content. I previously wasn't really shooting for microstock (I only became aware of this market in early January).
So far, this is the only accepted image that I had previously shot that was considered acceptable for microstock.