Sometimes the links posted on blogs and websites are not the actual link to the server but rather to the metatadata for the servers. If you have problems with the links you should open it in a web browser to see it's contents. If it is indeed just the metadata then you can usually find the WMS link address in that metedata. Just copy and past it into the Map WMS connection.
I have to disagree with you completely. FDO connection is much much much slower (to the point of almost useless) rather than attaching the image using imageattach.
The FDO raster is a joke on Map2010 3D. If you have a half an hr (slight exaggeration) to let it load when you zoom in you will be fine, but if time is precious and you want accurate placement. Bring the image in the fdo and mark the four corners. Then attach the image as an image and rubbersheet the corners of the image to the one that were marked on the FDO. This way, placement stays accurate and you get a much better response time once the image is inserted, plus other, non-map version of autocad can see the image this way....
One factor to consider when working with SID files is they use a compress/decompress algorythm to display the image and adjust the resolution as you pan and zoom your drawing. So while SID images are smaller and load faster than uncompressed images, they tend to slow down Autocad while you work.
The alternative is to use umcompressed images which use more disk space and take longer to load, but performance can be somewhat better once loaded since there is no need to decompress. There is also the option to use images that have been decimated to reduce file size (and quality). The challenge is to balance performance vs. file size and resolution.