Hey Padeen,
No need to purchase another device, but if you want to use the eTrex with Streets&Trips you will need GPSGate. S&T 2010 still insists on seeing the incoming data on a COM port running at 4800,n,1. Most GPS receivers supply a USB-to-serial driver that makes their devices show up on a virtual COM port so there has not been a lot of pressure for Microsoft to upgrade this aspect of S&T.
I just tried my eTrex Legend HCx (straight USB connection, no serial driver or other conversion) with Street Atlas 2010 Plus and it works fine with it. It's not automatic, though. You have to go into the GPS settings page, select USB, and select Garmin/Garmin (my Legend HCx only does Garmin protocol) from the list of supported Manufacturer/Protocol combinations (it also supports Garmin/NMEA on USB). The button turned green with a 3D lock in my basement office in under five minutes.
It obviously does not support the full Garmin protocol. When you switch to the Sat. Info display you get nothing, so it looks like it's ignoring all the data about which satellites the receiver sees, the almanac info and all the Dilution of Precision (xDOP) info. That's only of interest to geeks like me, anyway. It works great for navigation.
Terry, to check this with SA 2010, click the GPS tab. There are two icon buttons immediately below the "Clear Trail" button. Hover over the one on the right and it should say "Turn on/off various GPS features". You'll be impressed by the variety of USB devices SA2010 now supports.
Padeen is right: Products like Streets&Trips, Odyssey Navigator and iGuidance need to pull up their socks if they want to keep up with Street Atlas and Mobile PC in device support.
...ken...