For download of updates from ni.com such as the device drivers (http://joule.ni.com/nidu/cds/view/p/id/3145/lang/en/rating/1) NI recommends to use the NI Downloader.
First suggestion: Fine, but the Download tool should download all the relevant files in one operation.
Not as of now where you have to download one NI Download program for each of the (here two) "DVD's" and execute each of them to get both install images downloaded. It is error prone, tedious and requires additional installation instructions.
Second suggestion: Give the user an option to keep the download in one big file. I think it is very few users who actually need the files to fit on a space restricting storage medium. As a note I see from the latest LV2012 downloads that some of the installation distribution files are more than 8GB. 8GB would easily hold the device drivers (as of 2012) so there is actually no need in this particular case to span two media.