theres a few videos on youtube about it, but they are terrible, so I made my own.
Files you will need...
VMSBrowser.exe
A Dreamcast Save File
NullDC memory card file
Steps:
1. Create a memory card file in NullDC (assuming you dont have one... they are named "vmu_data_port##.bin" in your NullDC folder where ## = two numbers, most likely 01)...
-Open NULLDC
-File > Normal Boot > "NO DISC" button.
-Select FILE
-Should see a memory card with a big red X, select it and follow the steps to "Delete all (memory reset)".
-When you are done, you should now have a file in your NullDC folder "vmu_data_port##.bin", probably ## = 01.
2. If you don't have vmsbrowser.exe, you need it.
-Go to EMUParadise.me
-Emulators on the left side, Sega Dreamcast, Windows, download Chankast.
-Open the zip/rar file and find "vmsbrowser.exe"
-Extract it to your nulldc folder.
3. Download a save file for the game you want.
-Go to http://bswirl.kitsunet.org/
-"VMU Saves" on the left side, find the game you want.
-Use the dropdown box and select "DCI File (Nexus cards)", it will auto download.
-Rename the file (if you wish to) to the name of the game and put it in the NullDC folder.
Almost done.
4. Importing the save
-Rename your "vmu_data_port##.bin" file to "vms.bin". Remember the name of this file, you will need to change it back later. (Note: If windows is set to hide extensions of filetypes, just leave out the ".bin" part)
-Open VMSBrowser.exe and you should see on the left side "vms.bin"
-Click the top right button "Import Save" and select the save file you downloaded earlier.
-Close VMSBrowser.exe and it will ask you if you want to save, say yes.
-Rename "vms.bin" back to "vmu_data_port##.bin" or whatever it was called before.
5. Run your game!
You can keep doing this method and import various save files all onto the same memory card.
-Enjoy
SpatzST