Am I right in thinking..................

I think it has been "sorted out", but you need to pay attention before purchasing. There should be a link on Garmin's site on the page where you choose maps, "Which Format is best for me?"

iqc.garmin.com/.../request.do

Question: Should I purchase mapping for my GPS on a disc, pre-programmed datacard, or as downloadable content?
Answer:

Mapping for Garmin GPS devices is sold in a variety of formats. It may be purchased on a disc, as a pre-programmed datacard, and some maps can be downloaded directly from the Garmin website. Please see below for the benefits of each format.

DVD/CD: Maps purchased in this format will require a computer to use but they will allow you to plan trips on your computer and transfer waypoints, routes and tracks to your GPS device1. The installation process will install the mapping and the MapSource or BaseCamp application to your computer. MapSource or BaseCamp can then be used to send maps to either your device or a blank datacard since most devices will not hold all of the data on the device. Please note that most mapping products in this format are unlocked to a single device and they are non-transferable. City Navigator maps in this format can be updated by purchasing a map update, when available.

Pre-programmed datacards: Pre-programmed datacards are immediately ready to use out of the box. Simply unpack the card and insert it into your compatible GPS device. These maps do not need to be unlocked to your device which allows you to move the card to multiple units if desired, however, you will not directly have access to the mapping on your computer2. City Navigator maps in this format are not eligible for map updates and mapping from the card cannot be copied. If you wish to obtain updated content, a new card will need to be purchased.

Downloadable Content: Maps purchased in this format can be downloaded directly from the Garmin website. This is the quickest method of getting mapping for your next trip. Downloaded maps can be sent to either your GPS unit or a blank datacard since most devices will not hold all of the data on the device. All maps in this format are unlocked to a specific device and they can only be used on the device that they were unlocked to. Similar to the pre-programmed datacards, this mapping is not immediately available on your computer for use in planning routes2. City Navigator maps in this format are not eligible for map updates. If you wish to obtain updated content, a new download will need to be purchased.

Note: Before selecting your purchase option, be sure to review the requirements tab and products tab on the individual mapping product page to ensure your device and/or computer will work with the selected format.

1Not all devices are compatible with routing.

2Garmin's free BaseCamp application can be used to view mapping detail from compatible pre-programmed datacards or downloadable content on your computer. To find out if the map is compatible with BaseCamp, check the requirements by clicking the Requirements tab for the specific map product. BaseCamp can be downloaded at: http://www.garmin.com/garmin/cms/us/onthetrail/basecamp. BlueChart, BlueChart g2 and BlueChart g2 Vision downloads and pre-programmed cards can be viewed on your computer with Garmin's HomePort application. HomePort can be purchased at: https://buy.garmin.com/shop/shop.do?pID=64242.
Last modified on: 07/25/2011

However, to solve your immediate problem... copy the contents of the SD card to a USB flash drive and plug that into your computer. You should now be able to access the map without connecting the GPS or removing the memory card.

Also, there's an advantage to purchasing on SD cards because they aren't locked to a single GPS. The download and DVD versions will be locked to the first unit you install them on.