I am using stamps.com with Vista without problem but I am printing either to a USB Dymo Turbo 330 label printer or an Epson R220 on a remote XP box. There is a new version of stamps.com out so make sure you have the latest version, same thing for the Dymo label printer, The error message that you are getting sounds like a printer driver problem. Have you checked to make sure that your new printer is Vista compatible?
HTH
BillP

 I am running Vista Home Premium and can print with everything except Stamps.com Internet Postage.  When I use my HP Color Inkjet Business Printer cp1700 I gat "Processinbg Job" in the LCD display on the printer, but nothing ever prints.  So, I purchased a new printer, an HP Photosmart D7360.  Whre I try to print an envelope with is I get the message " Paper Size or Type Mismatch".  If I change the paper size and type to #10 envelope it prints and addresses and postage half size in the middle of the envelope.  

 Anyone else have problems with Stamps.com ?  Any suggestions would be appreciated.

 DigitalMale
 bwebbj@cox.net

I had the same problem running Windows Vista Ultimate. Here's what I
did. This should work on any short edge printer.

Select tools
Configure Printer
Next
Select #10
Yes
Next
When you see the picture of the Short Edge and Long Edge, Press
Ctrl+Shift together and then left click on the short edge icon. You
should get a drop down menu.
Select L90
Click OK
Now, follow the rest of the prompts and your envelope should print
fine.

Hope this helps.