Wait until the words "Hi Kids" appear on the screen and replace them with:
 
Rats       level 1
Carumba    level 2
Nuclear    level 3
Framed     level 4
Snotned    To choose the level yourself
 
(First you must run UNLZEXE on TD.EXE, TR.EXE, TXS.EXE)
Hex edit each.
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For unlimited energy:
Search for 2C 0A 2E A2 A3 0E
Change to: 90 90 2E A2 A3 0E