|Mike is correct is saying that's it probably better to use a VLOOKUP function, but to answer your original question as to why your formula doesn't work, think about how an IF statement does it's thing.|
It starts at the beginning and checks each condition. As soon as it finds a TRUE condition, it returns the value associated with that condition and stops checking.
Look at your third condition:
Since 75 is less than 98, that condition is TRUE, so your formula returns 1.25.
The trick is to turn the IF around and start with the lowest value first.
In addition, you don't have check every single value. Since you have "breakpoints" - 74.5, 77, 79, etc. - you can use these to set your conditions.
I can't check this many IF's in 2003, but I believe that this should work for you:
Format the cell to show 2 decimal points and you'll get 5.00, 3.00 etc.