Click & Drag Formulae Problem

I am having trouble working out what has gone wrong/what I have pressed to be experiencing the following. I'm knew to excel 07 as I have it as a trial but whatever I have done has effected my Microsoft Works spreadsheet as well.

I have a table that looks like the following.....
A B C D E F G
1 | PERIOD 1 10.0 |
2 | WK1 | WK2 | WK3 | WK4 |
3 | 2.5 |2.5 | 2.5 | 2.5 |
4 PRODUCE 500 | 12.5 | 12.5 | 12.5 | 12.5 |
5 BREAD 250 |
Problem 1 - Relates to cells D3, E4, F4 & G4
in order to get the 2.5 I entered the calculation...
in cell D3 I entered =g1/4 which gave me 2.5, correct, but when I clicked and drag this cell along for boxes E4, F4 & G4 the calculation didn't follow the source, ie the value of G1 but moves along so put in H1/4, obviously with H4 empty it didn't give a value. I'm sure excel used to know which cell you were talking about, ie the source.
Problem 2 - Relates to column D, again clicking and dragging the calculation, I'm entering =d3/100*A4 to get 12.5 which again is ok but when I click and drag down or drag to repeat the calculation across the table the formula takes into account the cell below therefore giving totally corrupt data. The only way I can solve it is to go back into each cell and change the letter back on part of the formulae, e.g bread should be =D3/100*A5 but drags as =d4/100*A4 and so the problem continues down the spreadsheet.

Looking at the attachment if you click and drag column C you'll see what I am talking about, if anyone can shed any light on what I've done wrong it would be greatly appreciated.