basically mate, people make the m3 lite out 2 be hard to use but its really simple.
basically u choose where your NDS roms are, then u choose where you want them saving to (micro sd card, i strongly recommened a Dane Elec 1gb micro sd card and also you will need a card reader, 5 quid off ebay)
then find ur rom, go to
www.m3wiki.com then compatability lists, and then find the game you want to put onto ur ds lite.
then click write nds in the m3 lite program, find the game, load it up, follow the instructions given to u on the m3wiki site; some roms only need trimming, but all u do is check certain boxes, usually most games u need 2 check the 4x dma box, the in game reset box and the trim rom box, and then click write, and it writes it to the card. it only takes a few seconds, as the games are fairly small.
its a piece of piss really mate, id recommend the m3 lite.