I tried looking into REIN r16, but couldn't get it to work w/ the DS Lite. What I ended up finding was ETool v3.13 which you can grab here:
http://nds.cmamod.com/files/ETool_v3.13.zip
If you open the ZIP, you'll see two files, ETool3.nds and ETool3.sav, in the bin/DS/Supercard folder. Put these onto your microSD card. Load up the ETool3.nds like you would any other ROM. After ETool loads, pop out your Superkey and put your game into the DS slot. Save the contents of the game file to SRAM. Put your Superkey back into the DS slot. Do a quick power cycle (turn off and on your DS quickly) to get back to the Supercard main menu. Select the Saver tab, find the ETool3.sav file and save the contents of the SRAM to the SD card. You'll have dumped your game's save file into ETool3.sav. Then, copy that onto your PC and drag the file onto the ETxtract.exe file in the /bin/PC/ directory of the original ETool ZIP you d/led. This will output a .sav file which you must rename to whatever your .nds game is. So, for abcde.nds, you must rename the file abcde.sav. Copy this .sav file back onto your microSD card, start up your NDS and start up your game. You should have your save state as if you were playing the cartridge!
Hope that helps.