I had the same questions and problem but finally found a solution.
I've used a Brother laser printer for years on eBay without problems, but I recently bought a Zebra LP 2844. But while I could set it up and print test pages, actual eBay shipping labels were not printing correctly. They would print on two pages, only half or less of the label per page. It was like it was really centered on 4 pages but I was only seeing the left two pages.
Here is the fix. Go here and follow what the last poster said:
http://forums.zfirm.com/showthread.php?9383-Printing-labels-with-Zebra-lp2844-in-Parallels
First, make sure it is installed on the Mac, then install it in Parallels following exactly what this person said. I did it and it works fine now.
I installed the ZebraDesigner Driver on Windows (download from the Zebra website). Install the printer, set it as your default Windows printer. Then install Bonjour as the thread says, and run Bonjour to set up the Zebra printer to work with both the Mac and Windows. If it doesn't show the Zebra in Bonjour, go into your Mac System Preferences and set the Zebra to Share Printer. Now run Bonjour. The printer will show up, follow the Bonjour instructions to set it up. I just selected the Zebra driver listed in Bonjour, didn't do what the thread says for finding another downloaded driver, and it works fine.
My eBay sample label still prints incorrectly, but the actual shipping label prints perfectly.
I did go into the printer preferences, set the Zebra as the default printer on Windows, and created a new Stock to use as the default size label - 4x6, and set the unprintable area to all 0.00, just name that stock 4x6 (or whatever size label you are using) and choose that when you print.
You'll also need to download and install Java Runtime Environment, which the eBay printing page for each label has the link.
Java has 4 pop up windows asking if it's OK to print the label and use the selected printer. That happens every time I print a label. Very annoying. But at least it works.
It still prints wrong on the Mac, but in Windows 7 on Parallels it prints correctly.