I got Dymos working on Windows 7. The first thing to bear in mind though, is that if you have tried once and failed, you need to run the uninstall program first, before trying again. You download it from the Dymo site where you got the 330 drivers.
Once you have done all that, try following this guide if you are still stuck. Its written for wireless usb adapters, but the same thing applies to anything really. I've posted this link a few times now, so sorry if its considered spam, but I found it really useful and it will certainly help here.
Puzbie LTD: Getting USB Wireless Adapters Working with Windows 7.