Regarding this topic, I have some updates. I have created two modules/addons that now print USPS postage as well as integrate seamlessly into X-Cart.
Endicia Integrator (by WorkingMan Software)
A module to allow essentially seamless integration of Endicia into X-Cart. Using Endicia's Dazzle under Windows, the software supports batch label processing.
The system allows you to upload the result file from Dazzle and then automatically updates the order status and the tracking number (if the print was successful). Endicia's Dazzle automatically checks the address and if it fails to verify properly, the system does not print it.
In batch processing, the system will verify and print all labels that have valid addresses. The result upload page will let you know which addresses had errors. (US Domestic Mail Only - global integration coming soon)
Here's a picture of 4-up labels on Avery 5168 label stock as printed automatically using WorkingMan's Endicia Integrator with X-Cart and Endicia's Dazzle shipping system.
http://www.workingmansoftware.com/wm_images/4up_labels_250x324.png
Mac OS X Endicia currently has a bug in batch processing address verification. However, the system still works by printing labels one at a time. The sytem populates the Endicia program automatically and you simply press "print". The drawback is that the order status and tracking number is not automatically updated in this mode. Hopefully, batch order processing will be working properly with Endicia's next Mac OS X release. (Technically, you can use it now, but it results in a slightly higher address information error rate).
http://workingmansoftware.com/content/view/24/60/
Video of system in action:
http://workingmansoftware.com/content/view/30/68/
USPS Automator (by WorkingMan Software)
This system utilizes the USPS Click-n-Ship website to print Priority Mail or Express Mail postage. It integrates fully into X-Cart - click submit, wait 10-20 seconds and the label pops up. (US Domestic Mail Only - global coming soon)
http://workingmansoftware.com/content/view/23/61/
Bothe of these software pieces are in active development. USPS Automator is in use at a number of sites currently and has excellent success.
The Endicia Integrator software has just surpassed version 1.17 and is working well.
Thanks,
--Nate