Your gps already HAS the maps you need installed!
The T in your model number denotes that your unit has a pre-installed topographic basemap. The Colorado 400t is preloaded with US TOPO 2008. It is a less detailed version of the full US TOPO 2008 vector map package, so that it all fits, but it is more than sufficient for navigation. Note, this is NOT the normal road basemap, but rather the vector topo maps you normally pay for from Garmin.
The trade-off is that, unlike the PN-40 (which comes with a full US vector map on DVD, but you have to load the maps on SD card), you have to have the full thing in memory all the time, AND you don't get a CD/DVD copy, as far as I've heard. But, for an out of the box experience, it rocks.
I've spent the weekend playing with the 400t and here are my thoughts....
1. In automotive mode the US Topo 2008 map is not capable of auto-routing due to the omitted data to save memory space. I had a drive from central Alabama to Rome Ga and the unit was very helpful, but I'd like it to be more user friendly. Example: To input a destination you have to pan across the map from where you are to manually select the general area of where you want to go. With the vector map you can input an address.
2. In recreational mode I tested the unit at Oak Mountain. The elevation info was interesting and being able to see water sources beyond my view was nice. I would still like to be able to download a map like Jaybird posted using tracks that are already marked. I realize that I can hike the trail and then I'll have the tracks and any waypoints I mark, but surely there is an already complete map with trails marked available.
3. Finding more information on the unit itself is difficult. I've searched the internet, including Garmin's site, and found very little clearly laid out information. It seems that most info on the web is geared more toward sales and reviews rather than support. It also seems that what support I find presupposes the user having previous knowledge of GPS and Garmin's operation.
All in all I think the unit is great. I just wish more information was available.