Load the game up and watch the demo (the screen that says "start infecting!". If you pick up the money, you get to take it into the game with you. Helps a little at the beginning.
If anyone's having a problem, raise STR and REP. Once you get to the cells that increase REP/STR/DEF, get those first, then attack from there. STR lets you take their cells with smaller numbers, and if your REP is up high you won't need DEF.