By making a game selfbootable I assume you mean a homebrew game. If not, then we do not give support on how to pirate commercial Dreamcast games. To make a homebrew game self boot, I suggest using DSSBS. (
http://www.ngemu.com/dc/dcgenerator.php?action=tools ). Basically just but the scrambled binaries ( 1ST_READ.bin and IP.BIN ) in the "new" folder, select what image you want, and burn. It is as east as that.