I just did this yesterday. It was really easy.
1) Install iTunes on the Surface Pro. Make sure to use the same iTunes account to access the iTunes store. \
2) On the Pro, create an \iTunes\Media folder on the MircoSD.
3) Assuming you have less than 64GB of music and movies on your desktop, simply copy the contents of your \iTunes\Media folder to an external HHD.
4) From the HHD, now copy the iTunes\Media folder to the MicroSD \iTunes\Media folder.
5) On the Pro, go into the iTunes Edit, Preferences. On the Advanced tab, change the iTunes Media Folder Location to match the \iTunes\Media folder on your MicroSD.
6) On the Pro, go into the iTunes File, Add Folder to Library. Browse and select all folders from the new \iTunes\Media\Music folder on the MicroSD and they will be imported into your iTunes library on the Pro.
For me, I had too many movies that I exceeded the 64GB space on the MicroSD card. Rather than import the entire iTunes Media folder, I removed the Movies folder and just copied the music. Since I used the same iTunes account as my desktop, the iTunes on the Pro had all my movies that I purchased. Now I can just download the movies I want since I already purchased them.
Hope this helps some of you.