Downloading a previously purchased app to iTunes on another computer I've purchased and downloaded an app to a computer that I do not sync with my iPhone on a daily basis. I would like to download the same app to a computer that I do sync usually and then sync it.

Is it possible, if no - is there any workaround?

I've purchased the app on a Mac and I wan't to do the sync it from Windows (both computers have the newest version of iTunes).
It is possible, there are a few steps required.

The other computer must be authorised to access that Apple ID.

On the iTunes store page on the right hand side, there is a Purchased option, click on this and all previous apps, movies, music, etc purchased will be shown. You can then download it from there.

Apple has a help page about this that can be viewed at http://support.apple.com/kb/HT2519. It is the bottom section.