If you're using version 0.47, you can use the Scatter extension for this, which is found under the Generate from Path submenu under Extensions.
- Create your path and the object you want to place along it.
- Select the object and press Home to ensure it is the topmost object.
- Select the object and the path.
- Open the Scatter extension: Extensions -> Generate from Path -> Scatter...
- You can play around with the settings. The most important one for your case is to change the setting near the bottom so that the original will be cloned instead of moved or copied.
- Check the Live Preview box to see how it will turn out.
- Press Apply when you're satisfied.
Oh, I just noticed you want the clones randomly spaced. Well you could do adjustments by hand afterward, or if you know some python you could edit the extension to perform random spacing.
I don't know of another way to do it automatically, unfortunately.