billythekidrock is right, you can only use garmin software with the gps.
Purchaes the Garmin TOPO and City Navigator, you will not be disappointed, they work excellent. Get a bigger memory card for it, if you have not done so (you can download the city nav and topo for the whole state if you have a bigenough memory card).
And you can send waypoits to the gps with other software but not maping software. I have pluged in my gps to my Lap top com. and tracked my movement on it in the woods (just for fun).
If you wnt the marien maps it will cost a bit more, but it show topo for the lakes and salt water. The regular topo has the topo for the Puget Sound and the Wa coast, you can see the depth of the water and other info also.
You have made a wise choice in GPS.