in some lowball games, straights count as high hands. 2-7 triple draw is one.
the nut low hand is 75432, 65432 counts as high hand.
for omaha 8b and s8b, the high and the low hands are evaluated seperately.
in Omaha and Stud 8b, 5432A is the nut low hand, but also plays as a straight for high. If you have

you also have a hand that plays for the low, plus a flush for the high.
you can also play different cards for the high and the low hand.
Play Poker Like the Pros is the best intro book for this game. Then Super System 2.