I would not recommend the update method recommended by Bris 1, as you may run out of disk space on your thin client and be up the proverbial creek. Go to www.wyse.com/kb and select the knowledge base tab. Search on the keywords "third party" and you should see an article on installing third party applications on Windows XPe and WES.
Follow the instructions and you should be OK.
Visit our Dell Wyse Thin Client Knowledge Base and Manuals web site at www.wyse.com/KB
Visit our Dell Wyse PocketCloud Knowledge Base and Manuals web site at http://pocketcloudsupport.wyse.com/forums